The influence of reactive power compensation on sensitivity of differential protection of ratio-restraining characteristic and product-restraining characteristic is studied, when the output line of grid-connected photovoltaic (PV) systems with low voltage ride-through capability occurs three-phase short-circuit failures. It is found that the use of LVRT results in the decline of two kinds of sensitivity of the differential protection. The model of grid-connected photovoltaic (PV) system is set up, and verified by Simulink simulation. And further conclusion shows that the impact of differential protection of product-restraining characteristic on sensitivity is smaller, when the reactive power compensation is injected, and is better for the protection of output lines of photovoltaic power station, when the short-circuit fault occurs. Finally, this paper presents recommendations about how to improve the sensitivity of the differential protection by the tuning mode of differential characteristic curve.