In order to meet people's needs of indoor fitness, a game system applied to the stepping machine is designed on the basis of a stepping machine in the market. It contains three parts:stepping machine, sensor equipment, and computer. The sensor equipment consists of two hall sensors, MAX232 serial port chip and STC89C52 single-chip microcomputer. The hall sensors find the pass of pedals and produce signals, single-chip microcomputer is used to calculate the step rates and send them, and serial port chip is used to transmit data to computer. The computer is used to run the game software and display the game images. The principle of the game software is that game protagonist's moving speed is determined by the average of step rate of left and right, and the directions of protagonist are determined by the difference of the step rate. The game of greed snake is adapted for the game system as test software, and functions of controlling snake movement and fitness are added in the test software. The game system can achieve the desired effect after repeated testing. The game system has good market potential because of its low cost of manufacture, easy manipulation and friendly universal property.