A power system stabilizer (PSS) is installed in pitch control system to damp low frequency oscillation of power system, taking into consideration of the stochastic uncertainty of system operating conditions. Cumulative probability curves are employed to obtain probability numerical characteristics of stochastic variables. The probabilistic method based on numerical analysis is used to study small-signal stability statistical attributes of power system with wind farm integration. Through simulation on a five-machine two-area system with wind farm integration, the effectiveness that a PSS is installed in pitch control system to improve probabilistic small-signal stability is verified, and the improvement of PSS is evaluated. Simulation results demonstrate that the installation of PSS in pitch control system could suppress effectively local oscillation and weaken inter-area oscillation.