Aiming at the issue of etalon effects in self-mode-locked lasers that affect laser output performance, a tunable-cavity-lengthNd:YVO4 self-mode-locked laser is designed. A single-end coated crystal is used to form an intra-cavity etalon for modeselection of the laser. The mode distribution of the spectrum and its corresponding timing diagram under different cavity lengthsare theoretically analyzed. The fluorescence spectrum temperature characteristics of the Nd:YVO4 crystal are experimentally verified,and its laser spectrum characteristics, the time trajectory of the mode-locked pulse sequence, and the spectrum distributionare analyzed respectively. The theoretical and simulation results show that when the ratio of the thickness of the etalon to the opticallength of the resonant cavity is a simple fraction of / , the longitudinal mode spacing can be modified to times the original,and a -order harmonic mode-locked laser is output. When the cavity length is 12.2 mm, and the ratio of the thickness of the etalonto the optical length of the resonant cavity is adjusted to 3/5, a high repetition frequency pulse laser output of 41.4 GHz isobtained. When the half-tube power in the vertical direction is 6 578 mW, the average output power exceeds 2.0 W, with the correspondingslope efficiency and light-to-light conversion rate of 31.2% and 30.7%, respectively.