This paper deals with the simplification and optimization methods in diesel engine control which is based on the air management system model of 1stage VTG and HP-EGR. Especially, simplified model based controller is suggested including more tracking performance of target values for comparison from previous multivariable sliding mode controller with intake and exhaust manifold output set. Moreover, in calculating desired exhaust manifold pressure, the simple process which only use target flow rates is suggested. There are fewer errors than general process's which have to add the target state process including the turbocharger parameter errors. Model based controller has assumption that mathematical model has to be very accurate, therefore, has to reflect the physical engine properties in every operating point. But, it is hard to satisfy this assumption because of the modeling uncertainties in mathematical point and a variety of environmental factor in real engine. Therefore, this paper suggests multiple sliding mode control with simplified process and robust scheme. And, this controller is verified in NRTC mode to analyze transient tracking performance, moreover, compared with previous 3rd order diesel engine model based sliding mode controller's performance.