Numerical solution models for simulation of the gas exchange process have been reported and in these models the method of characteristics have been used in order to predict the delivery ratio. However, computation of the pressure fluctuation in the inlet and exhaust ducts are complicated and seems to have no practical use from viewpoints of computation time and prediction accuracy. For the purpose of the efficient delivery ratio and suction air prediction in a reed valve type two-cycle engine, the crankcase pressure is calculated by the energy equations and the damped vibration equation. The method for prediction is presented using the calculated crankcase pressure and a reed behavior equation derived from the forced transverse vibration equation. Predicted values are compared with experimental values from a motoring test over a range of engine speeds from 200∼7000 rpm.