Abstract: It is of great significance for the industrial application of natural gas hydrate to promote the rapid and massive formation of natural gas hydrate. Gas-water ratio is a key factor influencing the formation of hydrate, so it is quite necessary to study the effect of gas-water ratio on the formation of hydrate. In this paper, a new mathematical computation formula for ideal gas-water ratio was proposed. Then, the effect of gas-water ratio on the formation of methane hydrate was investigated under 275.15 K and 6.6 MPa, and the accuracy of the new mathematical computation formula was verified. It is shown that hydrate formation rate increases greatly when gas-water ratio is higher than 1.8. Gas consumption is jointly determined by two factors, i.e., the initial amount of gas and the experimental phase-equilibrium pressure. The actual gas storage capacity of hydrate is more affected by gas-water ratio. Under the condition of ideal gas/water ratio, the formation performance of hydrate with sodium dodecyl sulfate (SDS) solution as the hydrating agent is in accordance with the calculated expectancy. To sum up, appropriate gas-water ratio can not only increase the hydrate formation rate, but also the gas consumption and the actual gas storage capacity of hydrate.