Abstract: Dynamic vibration equation of drilling string is established based on the theory of dynamics. Assuming that drilling string is an elastic straight pole, a geometric model is built. ANSYS software is used to analyze the characteristics of longitudinal vibration of drilling string and the influences of the position of vibration absorber placement on the longitudinal vibration of drilling string. The results show that properly positioning vibration absorber can alle-viate the longitudinal vibration of drilling string, thereby reduce or prevent drilling string breaking or splitting accidents.