This paper reports results of Tin doped fibre pumped by a semiconductor laser diode as an optical source for methane gas detection. The spectral characteristics of the Tm doped fibre pumped by the 788 nm laser diode is studied experimently and the fibre source is used in a correlation spectroscopy measurement system. With a short measurement cavity of 5.7 cm in length, a system noise level limited minimum detectable gas concentration of 0.47% is obtained. This value is far below the lower explosion level (5%) of methane gas. Thus it demonstrated the feasibility of using Tm doped fibre as an optical source for methane gas measurement.