This work presents a dynamic simulator for MSF desalination plants. It takes into account the heaters and stages dynamic, hydraulic, standard instrumentation and control systems. This simulator was developed to study the effects of faults that may affect a MSF system. In order to extend the results scope, the simulator allows the modification of MSF topology and parameters into a wide range. Indeed, it is possible to change the number of stages belonging to the recovery and rejection sections, controller parameters (set point, integral time and gain), valve size, pump characteristics, seawater conditions, stages and heater dimensions, etc. Since fault simulation is the main simulator goal, the model and its resolution were carefully designed to enhance stability and speed. The user can select the fault to simulate among a set of possible faults (fault in controllers, sensors, pumps, etc.), and can specify the activation time (at which the fault starts), the development time (time elapsed from the fault start up until the fault reaches its maximum magnitude) and the fault magnitude. Thus, it is possible simulate step and ramp perturbations. The simulator was tested with data from real plants and it has shown a good performance. To make the simulator operation easier, it was developed by using a visual language for Windows 95.