Based on pressure swing adsorption, Proportion Pressure Swing Adsorption (PPSA), a new enrichment method with high safety, was suggested to enrich the low concentration coal bed gas. A mixture of active carbon (CA) and carbon molecular sieve (CMS) was employed as adsorbent in the process of PPSA. The methane and oxygen in coal bed gas were adsorbed simultaneously. The experimental study was carried out in order to verify the feasibility of this method. The equilibrium adsorption characteristic of CA and CMS were tested. The results showed that both concentrations of CH4 and O2 in desorption gas could be controlled well and would not exceed the explosion limit in enrichment process by adjusting the mass ratio of CMS5/AC1. Therefore, the new method, PPSA, can guarantee the safety in enrichment of coal bed methane.