Reliability assessment of photoelectric conversion system can provide valuable reference for photovoltaic power station planning. Hence, this paper proposes a reliability assessment model of photoelectric conversion system based on Markov chain, which applies empirical criteria to classify temperature-irradiation state and construct its Markov chain, and then uses stress analysis method to calculate the failure rate of photoelectric conversion system, and then forms the Markov chain of photoelectric conversion system failure rate. Accordingly, the reliability indexes such as average failure rate of photoelectric conversion system are calculated, and the elastic coefficients of temperature and irradiation on the average failure rate of photoelectric conversion system are defined, which to quantify the sensitivity relationship between two meteorological factors on average the failure rate of photoelectric conversion system. Collecting the measured temperature and irradiation data of several observation stations in North Dakota, and evaluating the reliability index of a photoelectric conversion system at different observation stations. The results show that the average failure rate of the photoelectric conversion system at low latitude observation stations is higher, and irradiation elasticity coefficient for the average failure rate of the photoelectric conversion system is higher than temperature elasticity coefficient, the average failure rate of the photoelectric conversion system is more sensitive to irradiation than temperature.