The GO2/ethanol/water tripropellant evaporation and combustion in axisymmetric combustion chamber was numerically simulated. The different characteristics of the evaporation and combustion between dilative and traditional un-dilative entrance, and the different dilation-angles of the combustion chamber entrance are analyzed. The results indicate that the dilative entrance combustion chamber is benefit for thermal protection of the injection, and the flamelet backpedals with increase of the entrance dilation-angle. At the same time, that dilative inlet combustion chamber reduces the evaporation of the liquid component seriously. The evaporation rate decreases with the increase of the dilation-angle at first, but after the dilation-angle is bigger than a critical one, it increases.