This paper discusses that drivers press accelerator pedal mistakenly to cause malignant event in emergency. It is put forward to use AT89S52 MCU to design a controller that prevents from pressing accelerator pedal mistakenly. According to the standpoint of praxiology, this designation analyzes resoluble speed difference between vehicle accelerating operation and hard braking operation, as well as puts forward the design method of the controller and introduces its designation process of hardware and software.