In this paper, a series of steps for validating a Computational Fluid Dynamic (CFD) model of a novel impulse gas turbine generator is investigated. An impulse gas turbine generator is a small scale and compact electric generator designed to provide power to remote offshore platforms. The generator is driven by pressurized gas and generate power through expansion of the gas. As the effluent gas is designed to be redirected to lower pressure gas line, the generator provides clean energy with higher reliability and no dependency on weather if compared to solar panel technology that is widely used. As a new technology currently being developed and tested, the operating data of the generator is very limited, and the performance expected when deployed later cannot be ascertained. To ensure that the impulse gas turbine generator performs as per intended, numerical approach by using CFD is adopted where CFD model by using sliding mesh method have been developed. The simulations result is then validated with experiment results where the very small deviation is observed between the two results. With validated model, performance under natural gas or methane-rich condition is simulated and tested. Despite the different in gas composition, performance expected from CFD model is very similar to the actual result observed during the gas flow loop test.