Tuning of PID controller plays a major role in process control applications. Here we are going to control the level and flow of a three tank process. Three tank process is used in many industrial applications such as food processing industry, Concentration controlling etc., Controlling the level and flow is a difficult process since the non-linearity which exists in the process will not allow the parameters /system to be stable . Tuning of PID controller helps in achieving proper control of the process parameter and also ensures stable working of the system. Flow and level are directly interlinked with each other in process control application.