The influence of combustion chamber's shape on combustion process is studied，and the influence rule of the diameter of throat on spray penetration，SMD，turbulence energy，vorticity cylinder pressure，heat release rule and NO—SOOT are obtained．Moreover，The combustion reaction rate field， temperature field，concentration field and velocity field are compared and analyzed through 3 D method． The analysis results show that the diameter of throat should be kept in a rational range of 100～120 mm