Spur gear is machine element which is subjected to cyclic loading must be designed against fatigue. Spur gear failure is caused by crack is which depends on cause of design and operation condition. The main objective of this thesis is to develop a method for the investigation of initiation and propagation of cracks in involute spur gears using fracture mechanics approach and finite element analysis. Modeling of involutes spur gear to study contact stress created using SOLIDWORK Software and was imported to ANSYS software for analysis. Finite element analysis (FEA) is performed to obtain maximum stress point and life of spur gear using the ANSYS software with applying the boundary conditions. The maximum stress appears at the contact point of spur gear. The FE model of the spur gear geometry is meshed with tetrahedral elements. Mesh refinement are done on the spur gear, so that fine mesh is obtained on the contact point of spur gear, which are generally critical locations on spur gear. The failure in the spur gear initiated at the contact tooth of the gear, and fatigue is the dominant mechanism of failure. Geometry resulted stress maximum at contact point and the life of spur gear at the contact region 551.56, which is very small life. Fatigue safety factor is 0.11911 which is less than 1 at the contact pointe. Then the results of Von-Mises stress, shear stress, and life of leaf spur gear is done using ANSYS software results. The causes were eliminated by analyzing and understanding the manner it originates. Surface durability and tooth bending strength are two main factors that affect the service life of gears.