A comprehensive analysis model suitable for the helicopter with variable rotor speed is established. The model is able to calculate the rotor required power, trim controls, rotor hub vibration level and rotor noise of a helicopter in steady flight. And the flight data of UH-60A helicopter and related research results are used to validate the accuracy of the model. In order to provide the basis for the optimization design of rotor speed, the study is carried out to analyze the influence of variable rotor speed on rotor required power, trim controls, rotor hub vibration level and rotor noise. The results indicate that the variation of rotor speed have great impacts on the four characteristics above. 19.2% of rotor required power and 6.7% of rotor noise can be reduced by decreasing rotor speed properly, but at the cost of reducing the rotor control margin and increasing the rotor hub vibration.