The software design is one of the most challenging tasks during the design of a mechatronic system. On one hand, it has to provide solutions to deal with concurrency and timeliness issues of the system. On the other hand, it has to glue different disciplines (such as software, control and mechanical) of the system as a whole. In this paper, we propose a model-driven approach to design the software part of a mechatronic system, which consists of two major parts: systematic modeling and correctness-preserving synthesis. The modeling stage is divided into four steps, which focus on different aspects (such as concurrency, multiple disciplines and timeliness) of the system respectively. In particular, we propose a set of handshake patterns to capture the concurrent aspect of the system. These patterns assist designers to build up an adequate top-level model efficiently. Furthermore, they separate the system into a set of concurrent components, each of which can be further refined independently. Subsequently, the multidisciplinary and realtime aspects of the system are naturally specified and analyzed in a series of refinements. After the important aspects of the system are specified and analyzed in a unified model, a software implementation is automatically synthesized from the model, the correctness of which is ensured by construction. The effectiveness of the proposed approach is illustrated by a complex production cell system.