Abstract: Gas hydrate is an important potential resource in the 21st century.The hot spot in the researches of gas hydrate is to estimate methane resources in gas hydrate. Reliability of the calculating result could be reduced because of the uncertainty of calculating parameters when volume method is used to do the calculation,but the reliability of calculating result could be evaluated and described well and truly by calculating the frequency of samples using Monte Carlo(MC) method. After discussing the limitation of the volume method for the estimation of the methane resource in detail, the principle of the MC method for the estimation of the methane resource is researched and analyzed thoroughly, and the methane resource of gas hydrate area in Mackenzie delta is calculated as an example.