Abstract: In view of the problem that the existing measurement technology while drilling cannot solve the borehole depth measurement well, a high precision calculation method is proposed for the measurement depth while drilling of rotary drilling rig. This method uses the hydrostatic pressure at the borehole orifice as well as the borehole inclination angle and azimuth angle while drilling to calculate the depth, and the method does not need other special depth measurement equipment. On the basis of saving production cost, the method improves the calculation accuracy of borehole depth and is conducive to guiding the drilling construction. The experimental results show that the method can accurately measure the parameters of drilling depth without affecting the drilling operation, and accurately calculate the drilling depth in the process of drilling, which is more reliable than the traditional method.