Overloads in coach buses creates more possibilities to cause serious traffic accidents and bring heavy loss and injuries to our country and people. This research bases on sensor control technology and SCM (Single Chip Micyoco) technology in order to prevent people from changing its overload control system. We aim at developing an overload safety monitoring and warning control system which can count the number of passengers, send out overloading alarm signals and control the work of the engine. This system has functions that can set up upper limit of the number of passengers and show the current number. When the bus is overloading, the system will send out audible and visual alarm signals and stop the engine from starting through the engine monitoring system. When the overload is relieved and up to the upper limit, the system will automatically clear the alarm and the engine will return to its normal operation.