This paper studies two types of beat frequency tuning curve of 6328 A He-Ne20 transverse Zeeman laser. Relations of amplitude of beat frequency with cavity loss, total pressure and mixing ratio are given. The optimum magnetic field is introduced. The experimental phenomena of waveform distortion are observed. Choice of central beat frequency is studied. By PZT control the frequency stabilization is realized. Frequency stability of 2.5 × 10-9 can be achieved.