The power system stabilizer（PSS）based on wide area feedback signal is the primary means of damping control for low frequency oscillation of power systems.The operating conditions for wide area PSS，which prevent it from deteriorating stability，are one of the main concerns as its control effect for operators，but little，if any，has been reported on its investigation.With practical engineering applications as the backgrounds，three operating states，quit，operate and activate，and the states transition conditions between these states are presented.Three activation conditions are proposed at the same time，including local active power condition，climbing condition and frequency condition，corresponding to three kinds of special system situations，respectively，which are output changes of local generators，output changes of non-local generators，non-low-frequency oscillation situations.The following hardware in loop test using real time digital simulator（RTDS）shows that the combination of operating states transition and activation conditions can ensure correct operation of wide area PSS effectively.This study and testing results of operating conditions for wide area feedback signal based power system stabilizer is of practical value for wide area PSS application in the future.