The main goal of this research is the experimental and numerical study of the fatigue function and failure of the crankshaft of the diesel engine of a heavy truck. To this end, a crankshaft of the diesel engine of a heavy truck that underwent failure after traveling 955000 km was used. The crack developed from the third crankpin, leading to nal failure in the llet of the 4th crankpin. To investigate the roots of this failure, several experimental studies were carried out. Besides, by using a three-dimensional nite element method, the location of the maximum stress in the crankshaft was determined using \complete crankshaft model" and \one-crank model". The application of the results of stress analysis was the basis for the crack growth model and fatigue life estimation to determine the stress intensity factor and fatigue life considering the related parameters and boundary conditions. At the nal stage, by using the results obtained from the given model for the fatigue crack growth, comparing them with experimental results, and examining the whole process, it was concluded that the scratches in crankpin region were the main reason for the fatigue failure obtained from the bending-torsional load-combination.