Through analysis of existing key extraction methods of virtual keyboard for touch-screen mobile and physiological characteristics of thumb, a new extraction method of virtual keyboard was proposed. This method combines prompt box shows the information of buttons around the touch points, In the case of the first click has failed to acquire the target key, it use the sliding analysis to get the right target key. In this way, the error rate of the key selection was reduced and the speed of the correct choice was guaranteed. Theoretical analysis and experimental results show that this approach resolved the problem of Coverage and location ambiguity which was caused by using thumb to acquire the target key when the density of the target button is great and the button size is relatively small.