In order to research the voltage stability of power system including OLTC, this paper, which is based on the bifurcation theory, analyses the influence of load on voltage stability in single machine infinite bus power system including OLTC. Then, the function of OLTC in sustaining the system voltage stability and the influence of locking and delay in the regulating strategy and the equivalent reactance on system voltage stability are discussed.The results show that: when the system is close to the limit of voltage collapse, locking the tap of OLTC can sustain the voltage of load node at a relatively low level, which is conductive to avoid the system voltage collapse. And a short delay is effective in delaying the speed of voltage collapse. A smaller equivalent reactance will lead to a more obvious interferenceSreceived byStheSsystem voltage.