Abstract: The influence of C3 content in the feed LPG on the process for producing high purity isobutane was analysed, and the depropanizer tower was simulated and optimized using Aspen Software to get the suitable feeding position and reflux ratio. The results showed that the C3 content in the feed LPG has an effect on the energy consumption of the unit,the pressure and reaction performance of the hydrogenation system. The post C3-cutting process was suitable for the feed with C3 content lower than 20%, and the prior C3-cutting process was suitable for the feed with higher C3 content.