On the basis of the investigation on the rate equations of the Q-switch simultaneous dual wavelength laser of Nd:YAlO3(Nd:YAP), we have developed a new configuration of the cavity by adjusting the ratio of the cavity lengths for different wavelength lasers according to their emission cross sections. Therefore, the competitive ability and the net gain for the two different wavelengths will be equal at anytime and anywhere in the laser rod, and the optimal spatial and temporal overlap of the two different wavelengths can be easy to realize for optimal sum frequency mixing. In addition, 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.