This paper proposes a novel and robust power system (PSS) stabilizers simultaneous coordination method to ensure small signals stability and provide assessment transient stability for a multimachine system. Phase compensation is determined a priori using a sequential method and gains coordination is solved as an optimization problem. To reduce the complexity of this nonlinear multivariable optimization problem, a novel decomposition is performed, which allows an explicit objective function (OF) to be obtained based on the PSS’s gains. Finally, the practical application’s method is tested in the two-area benchmark system to demonstrate that it responds to the industry requirements.