Abstract: The guide wheel shaft of linear motor pumping unit in LN3-2-6X well fractured in use. The fracture causes of the guide wheel shaft were analyzed by macroscopic observation, nondestructive testing, mechanical properties testing, chemical composition analysis and metallographic examination. The results show that the guide wheel shaft beers alternating load during service, resulting in fatigue fracture. The cracks originated from the welding of the outer surface of the axle and the web. The unqualified mechanical properties of axle materials, abnormal microstructure of materials and poor welding quality of webs played a certain role in promoting crack propagation.