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A universal phase mismatch compensation method, which can be applied to temperature-insensitive frequency conversion, is experimentally demonstrated. In this method, two nonlinear crystals and an electro-optic crystal are cascaded. The generated phase mismatch in the nonlinear crystal can be well compensated for in the electro-optic crystal, thereby improving the stability of frequency conversion. In the proof-of-principle experiment, temperature-insensitive second and third harmonic generation (SHG and THG) are investigated by cascading KH₂PO₄ (KDP) and KD₂PO₄ (DKDP) crystals. The experimental results show that the temperature acceptance bandwidths of SHG and THG are 2.1 and 2.3 times larger, respectively, than that of the traditional method employing a single crystal. Meanwhile, the effectiveness of this method is also analyzed at a high power density, and a solution for the case of a nonuniform temperature is also discussed. Furthermore, angle-insensitive SHG is demonstrated to prove that this method can significantly reduce the influence of various unfavorable factors on frequency conversion. The demonstrated method may have potentially important applications in the nonlinear optical frequency conversion system.