The organo lead trihalide perovskite has shown to be an efficient material in solar cells while the stability problem remains a major drawback which prevents its real application.We demonstrate that the stability of the CH3NH3PbI3 film against moisture can be substantially improved through a modified chemical vapor transport(mCVT)synthesis approach.The crystal structure, light absorption and corresponding solar cell efficiency show no degradation after storing the mCVT-prepared perovskite film for up to 100 days in ambient condition with 40% relative humidity, which is greatly improved compared with the convention solution processed ones that are stable for less than 20 days.