A quasi-linear dynamic model for turbocharged diesel engine developed for control analysis and design is described in this paper. Linearized equations are obtained for the governor, the turbocharger, the combustion process, and the engine, taking into consideration the variation of the essential parameters over a wide range of the operating conditions. The model uses as its basis the steady state characteristics of the engine at the beginning and end of a change in input or load demand. The changes from one stale to another are characterized by linear transfer functions of either constant or variable parameters. Thus, the quasi-linear model developed, while retaining the advantages of the linearized approach, extends its capability in transient performance prediction of the engine over a broad operating range. Good agreement of computation results is obtained between the simulation model based on this quasi-linear approach and that based on the detailed thermodynamic cycle simulation. Applications of this model to the engine control analysis and design are discussed.