Keyboard is the most important equipment for computer appliance. However, improper design of keyboard will cause some symptom likeUlnardeviation and Radial deviation. My research goal is discovering the most suitable size of keys to promote the working efficiency as a simple conference. At the beginning, I picked 49 subjects randomly, investigating of the total length, width, the size of the letter key, the index finger width, and thickness of the keyboard. Among all subjects, the letter keys 1.3 * 1.3 cm and 1.5 * 1.5 cm are the most common. Then I chose 18 samples randomly to operating three kinds of keyboard (1.3 * 1.5 cm, 1.2 * 1.4 cm, 1.5 * 1.5 cm) in one minute to the most suitable size of keys.The resultreveals thatthe efficiency of size 1.3 * 1.5 cm and 1.2 * 1.4 cm is similar, but 1.5 * 1.5 cm is obviously typing inefficient. As for typing error rate, there is no significant difference.