A trajectory sensitivity-based generator parameter robustness estimation method is proposed， which can be used in online applications. Firstly， trajectory sensitivity is used to form the parameter set which has a relatively strong influence on a power system's dynamic behavior. An exponential type objective function is used to formulate the estimation model， which can automatically compress the bad data. A trajectory sensitivity-based method using phasor measurement unit（PMU） data is also presented to solve this model. The validity of the method proposed is proved by numerical tests on a New England system.