The gas saturation in flushed zone of gas layers is low and the observed gas signal is weak because the mud filtrate invasion reduces the native gas saturation. A (T2, T1/T2) two-di-mensional nuclear magnetic resonance (NMR) method of typing gas layers was developed. The performance of (T2, T1/T2) method for typing gas at different kinds of reservoirs, signal-to-noise ratios and gas saturations was studied in details through numerical simulation. The results show that (T2, T1/T2) method is especially useful for identifying gas formations. It is suitable for typing lower gas saturation formation where drilling mud filtrate flushes strongly.