The method for third harmonic generation of double wavelength and double pulse laser is proposed. Two pulsed laser beams with different wavelengths are reflected to make them near close and passing through two BBO crystals. Two wavelength second harmonics (SH) of laser pulses are generated after two times passing through the BBO of SHG. SHs and laser fundamental waves pass through the BBO of third harmonic generation (THG) to obtain two wavelength THGs, and couple out by 45° output mirror. The four phase matching conditions are analyzed to be satisfied in SHG and THG. This method can be used to intracavity THG of double wavelength and double pulse laser. The corresponding experimental results are given.