为了获得较好的激光性能，研究了直接与间接抽运对自倍频(SFD)激光性能的影响。建立了自倍频激光模型，并与已有的实验结果进行分析比较。利用该模型分析比较了直接与间接抽运下Nd3+YAl3(BO3)4(Nd3+YAB)自倍频激光性能。结果表明，当晶体的Nd3+浓度和长度的乘积低于一个特定值时，直接抽运获得的自倍频激光输出低于间接抽运，这表明直接抽运并不适用于任意浓度和长度的Nd3+晶体。给出了特定实验条件下适用于直接抽运要求的晶体浓度和长度。对其他自倍频晶体和不同的实验条件，采用类似的方法，也可以得到适用于直接抽运要求的晶体浓度和长度。

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.