Aiming at refractive index homogeneity of space flexible optical polyimide membrane, it can be measured through reflected wavefront of the substrate for preparation of polyimide optical membrane, reflected wavefront of up-surface of the membrane before being released from substrate and the transmission wavefront after the membrane released from substrate. Compared with data measured by the prism coupling, the results show that the proposed method is efficient and reliable for refractive index homogeneity measurement of flexible membrane in fully-aperture.