In recent years, with the widespread application of reactive power compensation equipment in power system, the issue of sub-synchronous oscillation brought by the reactive compensation equipment has been increasingly emerging. Based on the first IEEE standard system model for sub-synchronous resonance, this paper provides the power system’s model with shunt reactors, and the small signal model of the whole system is obtained. In addition, the eigenvalue analysis method is used to demonstrate the influence of shunt reactors on sub-synchronous oscillation in power system. It also discusses the effect of different shunt reactors values on the torsional vibration mode of the shaft system. As a result, the 10-generator 39-bus system of PSCAD simulation software is used to verify that the existence of shunt reactors makes the power system more likely generate sub-synchronous oscillations. Meanwhile, the reduction of shunt reactors value will increase the damping of the system. This work is supported by Sichuan Major Research & Development Project (No. 2017GZ0054).