Abstract: Power system steady stability situation assessment based on the wide were measurement system（WAMS） has great practical significance. The actual operation data generated by the power system are analyzed and a big data fusion method for steady stability situation assessment based on random matrix theory was proposed. The two limit spectral distribution functions（Marchenk-Pastur law and ring law） in power system steady stability situation assessment principle were proposed. On this basis, the linear eigenvalue statistic, such as mean spectral radius, was calculated as assessment indicator. Simulation based on IEEE 39 system verified the effectiveness of the method. The method can be used for steady stability situation assessment of power grid and it has the following advantages: unnecessary to build detailed physical models; able to consider the historical data and real-time data at the same time, and see the complex systems from the perspective of high-dimensional, etc.