An innovative piston error detecting and close loop correction method based on pyramid wavefront sensor was proposed for space optical interferometric telescope. Three different wavelengths are used in turn in the method, in which the pyramid sensor is used to measure the piston errors between sub-mirrors, and then the sub-mirrors are controlled to compensate the corresponding piston errors based on the real-time measurement results until the piston errors reach an integral multiple of half of the used wavelength. After that, the real values of piston error are calculated based the known data of wavelengths and quantities of piston compensation of sub-mirrors, and finally the piston errors can be controlled by closed loop correction. The proposed method was analyzed theoretically and researched by simulations in which a telescope with two sub-apertures was taken as research object. The results proved that the piston error between two sub-apertures can be soundly detected and corrected while the piston error is not more than 500 μm. In addition, the novel method meets the precision of nanometer and has good repeatability.