Research on intra-cavity second harmonic generation using periodically poled stoichiometric LiTaO₃ (PPSLT) based on quasi phase matching (QPM) is reported. Periodically poled crystals with different lengths (3.5 mm,5 mm,10 mm) are compared and examined. For the 3.5 mm PPSLT,1445 mW fundamental wave of 1064 nm could be achieved in condition of 2500 mW pump of 808 nm,then 760 mW green light of 532 nm could be achieved through second harmonic generation (SHG). Problems on system temperature control that affect SHG efficiency are also analyzed.