A 3.09 W sodium guidestar laser with the sum frequency generation efficiency more than 35% is reported.The laser is based on the periodically poled stoichiometric lithium tantalite(PPSLT) crystal quasi-phase-matched sum frequency generation.Two acousto-optical (AO) Q-switched diode pumped Nd:YAG lasers of 1064 nm and 1319 nm are used as the fundamental-frequency lasers.To get the narrow linewidth output,the etalons with well temperature controlling are inserted into the cavities.The sodium guidestar laser is generated through an external-cavity quasi-phase-matched sum frequency PPSLT crystal.When the total power of 1064 nm and 1319 nm is 8.80 W,the output sodium guidestar laser′s power is 3.09 W with the highest sum frequency generation efficiency at the matching temperature of 68 ℃.The repetition frequency of the laser is 800 Hz and the width of pulse is about 60 ns.The linewidth is about 1.6 GHz.The central wavelength is locked to sodium D2a line 589.1591 nm (error less than ±0.2 pm) by tuning the angle and the temperature of the etalons.