Like wind power generation，the randomness and intermittency of solar photovoltaic（PV）power generation increases the complexity and uncertainty of the system operating reserve assessment.The main factors causing the randomness of the solar irradiance are taken into consideration to establish the energy conversion model of solar PV.Simulations are conducted based on this model，and instantaneous transition probability of power output from PV in typical season and period of time is investigated.Finally，operating reserve of a reliability test system integrated with solar PV is evaluated through the extended PJM method.The assessment results show the capacity contribution of grid-connected solar PV in different seasons and time intervals in a regular way.