The present study relates to fracture mechanics and its aim is to find the effect of temperature on fatigue crack propagation under constant amplitude loading. The thermo-mechanical uniaxial and biaxial-planar fatigue behavior of the structural steel was investigated for constant amplitude loading at room temperature and between temperature range 673K and 923K. A fatigue analysis has been done for cruciform specimen using ANSYS 15.0 to find out the crack propagation and life of the material at different temperatures. A comparative study between the results obtained from ANSYS 15.0 and experimental results has been done to validate our analysis. A change from a mainly transgranular fracture at 673K to a mostly intergranular fracture at 923K was found under thermo-mechanical fatigue loading. Effect of temperature on crack propagation is presented which gives the best life prediction.