This paper describes a new way to stabilize the frequency of a Zeeman He-Ne gas laser. The laser frequency is stabilized by controlling the refractive index of the laser plasma. It dose not need a gas laser tube with a piezoelectric ceramic (PZT) made by special technology. As the phase-locking technology is used in the laser servo system, the self-beat frequency is a constant and the frequency stability is better than 2.2×10-11 (averaging time =10 sec.). The long term frequency fluctuation never exceeded 2×10-8 during two months. The frequency of the locked point can be adjusted continuously in the range of over 200 MHz.