Direct drive electro-hydraulic servo rotary vane steering gear is new high efficiency energy saving and high power density steering gear.In order to obtain performance parameters of this steering gear accurately,a mathematical model for it is established,and the exponent number of the model is determine,then searching is performed for the best parameter values between the upper and lower bounds of the parameters using a new identification method based on ant colony optimization-genetic algorithm(ACO-GA).The goal is to make the calculating output approach to the experimental one.The model is also verified by another group of experimental data,and the result shows that the close ratio is over 87%,which proves that the model parameters identified are reasonable.