In order to design optical system to collimate laser beam, its far-field distribution should be acquired exactly. Based on the Helmholtz equation, two decentered Gauss beams are used to represent the distribution of the source in the direction of paralleling the chip plane, then a new model describing the double-peak beam of high-power laser diodes is presented. A comparison with several practical devices is also made, satisfying result has been obtained, the rate of the error power to the total is only 1%～2%. Because of its simple structure, this model can be used to design shaping system or analyze the propagation properties when the laser beam passes through a optic system, and helpful for calculating coupling efficiency.