With the increasing of number and capacity of photovoltaic power stations connected to grid, its impact on the relay protection and control of the power grid can’t be ignored. Building the photovoltaic power stations’ electromagnetic transient simulation and equivalent calculation model is the basis of the grid-connected characteristics and the influence on relay protection. This paper introduces the common form of photovoltaic power station connected to grid, establishes a photovoltaic power generation unit model based on single-stage inverters, then builds a photovoltaic power generation system electromagnetic transient simulation model on PSCAD / EMTDC to verify its validity in steady and transient conditions. On this basis, the equivalent calculation model of the photovoltaic power plant consisting of photovoltaic power generation unit is given, and its validity is verified by the simulation.