According to a coal mining enterprise who urgent needs analyze how SVC device influences the stability of whole system, this paper proposes a SVC stable analytic method which is based on stability boundary theory of semi-tensor product. Apply the semi-tensor product stability boundary theory to the a coal mine 10kV distribution network which installed SVC devices. According to the actual situation, analyze the system stability margin index, establish a mathematical model which judges the stability of the system, besides use the Matlab software to simulate the whole system, finally obtain how SVC devices influence system voltage stability. This plan not only simplifies the calculation, but also can judge the stable degree of system based on the stability index. It has a strong reference value which can judge the stability of the system.