In optics tracking and detection system, frequent autofocus always result in shake of axes, which will cause image to wobble. A new algorithm that can estimate current frame image of optic equipment be in focus or not is proposed in this paper. According to current image be in focus or not and corresponding threshold, optic control system can choose the time of auto focus automatism. The algorithm measures object edge and edge direction, then get several grads points along the normal line and calculate edge sharpness value. Based on the measure precision of optic-equipment, a threshold value will be set beforehand. If edge sharpness value is more than threshold value, it can conclude current frame digital image is in focus. If image is out of focus, optics system then takes autofocus program. This algorithm test several thousands of digital images be get from optics tracking and detection system, the result shows that correctness of this algorithm is more than 93%. It can finish processing one image during the time of 2 ms.