Based on the rate equations of the Q-Switch simultaneous dual wavelength laser (SDWL) of Nd∶YAlO3 (Nd∶YAP), we have developed a new configuration of the cavity by adjusting the ratio of the cavity lengths for lasers with different wavelengths according to their emission cross sections. Therefore the competition ability and the net gain for the two different wavelengths will be equal at any time and anywhere in the laser rod, and the optimal spatial and temporal overlap of the different wavelengths can be easily realized for optimal sum frequency mixing. Besides, this configuration can overcome several disadvantages of the previously used configurations, and its photon density product integral of the two different wavelengths is about one order larger than the previous ones.