In the past, petroleum pipe thread was mostly measured by thread gauge, which was inefficient and easily affected by human factors. A noncontact measuring method on machine was put forward to handle those problems. Based on laser triangulation principle, a high precision laser, which was installed in a way of specular reflection, was used for measuring internal and external taper thread, and then using sliding window selfadapting Lyite Criteria algorithm, removed the jump point from the measured data. Afterwards, the thread tooth profile data was obtained through linear fitting by method of least square. Other parameters of the thread were calculated by the thread profile data, and measuring internal and external pipe thread on machine was achieved in this way. Compared with the previous one, this method has the advantage of high accuracy, high efficiency, less influenced by the human factors, and it made breakthrough in the measurement of internal thread by high precision laser.