When the large aperture off-axis three-mirror anastigmat (TMA) is launched to space, surface degradation appear on the the optical surface of its components due to gravity unloading, which will affect the imaging quality of the system. In order to ensure the imaging quality of the large aperture space reflecting telescope in orbit, it is necessary to explore the surface figure error compensation mechanism of the position of optical elements. Then the compensation mechanism of the secondary mirror position for the primary mirror and the third-mirror shape of the off-axis TMA system was investigated. So that the space telescope can actively use the element pose adjustment to compensate the impact of surface figure degradation on the imaging quality of the system.In order to analyze the progressive compensation mechanism of the surface figure error, the compensation mechanism and compensation amount are defined and calculated based on the nodal aberration theory（NAT）. Firstly, the Zernike polynomial vector form is used to describe the surface figure error of the off-axis TMA system based on the vector multiplication rule, and its derived aberration distribution is analyzed. Different from the aberration characteristics of the position of the primary mirror at the stop, the third mirror in the non-stop position of each field of view on the surface of the beam trajectory is different (Fig.1). Therefore, when compensating for the surface figure error of the third mirror, the situation of each field of view is different. This is also the focus of the investigation on the analysis and discussion of using pupil position transformation and least square method to solve the problem. Then a vector aberration correction model is proposed and an aberration compensation model of off-axis TMA system is constructed. In order to objectively evaluate the imaging quality of the imaging system, the exit pupil wave aberration RMS value is taken as the evaluation standard, and the secondary mirror adjustment with small aperture and the highest sensitivity in the TMA system is used to compensate the system exit pupil wave aberration with surface figure errors in the primary mirror and the third mirror.Simulation experiments show that when the primary mirror of the system has 0.5λ astigmatism and coma, the constructed aberration compensation model can compensate the exit pupil wave aberration RMS value from 0.18λ to 0.08λ (Tab.5). When 0.05λ astigmatism and coma exist on the system's third mirror, the exit pupil wave aberration RMS value can be compensated from 0.3λ to 0.1λ (Tab.8). In order to verify the applicability of the aberration compensation model, Monte Carlo experiment was carried out, which proved that when the third-mirror figure error (astigmatism and coma) was within the range of (-0.03λ, 0.03λ), the RMS value of each field of view of the system could be compensated to the design value of the system (Fig.9). A portable surface figure error compensation model of the TMA system is designed. It can compensate the RMS value of the TMA system with 0.5λ in the primary mirror and 0.05λ in the third mirror respectively to the nominal state. Through analysis, it is found that the third-order coma in the non-stop position is derived from the linear correlation astigmatism with the field of view by optical symmetry coordinate transformation. The astigmatism and coma distribution rules can be verified during the analysis of the surface error of each position of the system, which provides a theoretical reference and basis for other types of aberrations and further theoretical guidance for the active in-orbit installation of large aperture reflecting space telescopes. It provides the basic theory and framework for constructing the surface figure error compensation model of the primary mirror and the third-mirror of off-axis TMA system.