A simulation system, which can be widely used to determine the starting times of operations for general batch plants, is proposed. The operations of a batch plant are first expressed by a sequence of basic operations such as filling, processing, discharging and cleaning. By using these basic operations, the simulation problem can be reduced to that of determining the starting times of the basic operations. A variety of constraints are grouped into four types, and it is demonstrated that the constraints on finite intermediate storage can be converted into the constraints on precedence relationships of basic operations. Then, for each of the three types of constraints, simulation modules to calculate the earliest and latest starting times of basic operations are developed. A simulation program to calculate the starting times of basic operations which satisfy all types of constraints can be generated by combining these simulation modules. The major feature of the proposed method is that the simulation program can be easily modified by recombining the simulation modules. Therefore, a simulation program with sufficient flexibility can be developed by using the proposed method.