In the field of optical surface shape detection, the use of space carrier phase shift technology can realize the rapid and dynamic measurement of the surface shape to be measured, and the introduction of systematic error has always been an important factor restricting its accuracy. In order to solve this problem, this paper proposes a method for adaptive introduction of optimal systematic error. This method realizes the introduction of different carrier amounts for different specifications of the mirror to be tested, controls the system backhaul error within a reasonable range, and improves the accuracy of space carrier surface shape detection, and the process can be summarized as follows: First, estimate the PV value of the mirror to be measured. The default of the plane mirror is 0.3λ, and the spherical mirror calculates its PV value by obtaining its radius of curvature R and aperture ϕ, and substitutes the PV value calculation formula; secondly, the weight of the system backhaul error is equal to the weight of the PV value of the mirror to be measured; finally, the inclination angle of the mirror to be measured is inferred and the number of carrier fringes through the system backhaul error calculation formula, and whether the value range of the number of carrier fringes is judged. Experimental results demonstrate that, compared to the fixed fringe method in traditional spatial carrier techniques, this method improves the detection accuracy of flat mirrors by approximately 10% and the detection accuracy of spherical mirrors by approximately 15%.