Abstract: Directional drilling technology of measurement while drilling is widely used in underground coal mine for drilling trajectory controllability. According to the measurement method of drilling trajectory and measurement error, this paper introduces the calculation method of directional drilling trajectory, than analyzes the reasons of measurement error and effects. Some measures can be taken to reduce the influence and to improve measurement precision of borehole trajectory, such as improving instrument precision, regulating grid convergence angle, accurate metering hole depth and reducing magnetic interference.