In order to obtain best laser performance, the effect of the direct and indirect pumping ways on the laser output is studied theoretically. A self-frequency-doubling (SFD) laser model is developed. The calculated results are compared with the reported experimental results, and it verifies the validity of the model. Based on the model, the Nd3+YAl3(BO3)4 (Nd3+YAB) SFD laser performance under the direct and indirect pump ways is studied theoretically. As the results show, for some Nd3+ concentrations and Nd3+YAB crystal length, the SFD laser power of direct pump is lower than that of indirect pump, and it implies that direct pump is not suitable for all samples. The criterion determining which sample is suitable for direct pump is given. By the similar process, the criterions for the different SFD crystals and experimental parameters could be derived.