In grid-connected photovoltaic system, the inverter, grid device, power electronic devices etc. They consume a large quantity of reactive power; mostly in distribution system, a perceptual load must also consume reactive power, these makes big interference interconnection of photovoltaic system after serious test the voltage stability. Therefore, carry on research of voltage stability in grid-connected photovoltaic system has important significance. With the voltage stability, voltage quality, analysis the possible influence of photovoltaic grid power system on power grid in safe and stable operation. Discuss probable bifurcation behavior in photovoltaic grid system. Introduce the basic concept of bifurcation, and then review the application of bifurcation theory in research of voltage stability from two aspects: static bifurcation and dynamic bifurcation. Finally take a look at bifurcation theory research of photovoltaic grid system voltage stability.