The modular simulation model of MW-level grid-connected photovoltaic (PV) power station is established at PSCAD/EMTDC. In this paper, simulation models according to different real engineering can be set up based on the modular flexible combinations. Next, power quality of PV power station and influence on distribution networks are studied. In addition taking a real system for example, the voltage deviation and the harmonic distortion (THD) of distribution networks connected with the different scale grid-connected photovoltaic power station are analyzed. The conclusion that voltage deviation of distribution networks may exceed limits of national standard with the expansion of PV capacity is drawn. This paper puts forward reactive power control method of the station based on synchronous PI current control. Finally, the harmonic current generated by the 10MW PV power station is analyzed.