By studying the polarization characteristics of the birefringent Nd∶YVO4 crystal, a novel birefringent filter comprising an Nd∶YVO4 laser crystal with a wedge angle of 10° and a frequency doubling KTP (potassium titanyl phosphate) crystal is constructed in a green laser. The influences of the KTP length, incident angle of the fundamental mode in the KTP, and KTP temperature on the electing-mode function of the birefringence filter are theoretically analyzed. In the experiment, KTP crystal with lengths of 4.4, 5, and 7 mm and containing V-cavity structures are used, and 90-, 120-, 104-mW single-frequency green light is obtained, respectively. Experimental results prove that the birefringence filter comprising a wedge Nd∶YVO4 and KTP can successfully realize laser single-longitudinal-mode operation. Further, the proposed method is simple and easy. For 5-mm KTP length, the single-longitudinal-mode operating temperature range of the wedge Nd∶YVO4/KTP laser is measured to be approximately 5 ℃.