This paper deals with the speed synchronization controller design for networked integrated motor-transmission (IMT) powertrains via controller area network (CAN). It is well known that, in current implementations, CAN has been widely used in the control system design of automotive powertrains. However, on the other hand, the application of CAN would not only lead to network-induced delays but also bring about protocol constrains, e.g., data package capability and utilization ratio limitation, which would deteriorate the system and make the controller design a challenging problem. This paper is to provide a co-design methodology that can cope with all these problems and ensure satisfactory control effect for the speed synchronization control of IMT powertrain systems. First, a networked IMT powertrain system using CAN as underlying network is presented and the dynamic model for the speed synchronization control is derived. Second, the network-induced delay model is introduced and improved considering data packet capability and utilization ratio limitation. The control-orient discrete-time model is also derived based on the improved delay model. Third, a co-design methodology using sliding mode controller and offline priority scheduling based on Lyapunov stability criterion is proposed. The results of simulations and tests show the effectiveness of the proposed co-design methodology.