The experiment and AMPS modeling have been used to analyze the characteristics of a-Si solar cells on flexible substrate with different buffer layers at the i/p interface. Combining with technology parameters, this paper uses different band gap and the defect density of states of the interface layer to simulate the characteristics of solar cells. The modeling results show that the solar cells are deteriorated by the interface layer with a big band gap and large defect density of states. By optimizing treatment of i/p interface, the amorphous silicon solar cell on polyimide substrate has been achieved with an efficiency of 7.09%.