FeCrAl alloy is one of the candidate materials for reactor fuel cladding due to its excellent oxidation resistance at high temperature. However, the presence of Cr and Al has negatively effects to the mechanical properties and pose a potential risk to the safy of reactor operation. In order to analyze the deformation mechanism of FeCrAl alloy system in microscale, the mechanical properties of FeCrAl single crystal under the influence of temperature and strain rate were studied by molecular dynamics method. The defects distribution, dislocation density change and deformation mechanism are discussed, and analyzed the solute atoms on the result of simulation. The results show that the increase of temperature increases the thermal motion of atoms, promotes the formation and growth of defects, reduces the interaction between atoms, and results in the decrease of elastic modulus and tensile strength. The increase of strain rate leads to the decrease of elastic modulus and tensile strength. The plastic deformation mechanism of low strain rate is mainly deformation twinning, of middle strain rate is dislocation slip, and of high strain rate is deformation with atomic arrangement disorder. The effect of temperature and strain rate on α-Fe and FeCrAl is similar, but Cr and Al in FeCrAl cause significant lattice distortion and stress concentration, promoting the formation and movement of defects and dislocations and reducing the yield strength and tensile strength. Based on the calculated results, a constitutive model for FeCrAl crystal system was established based on Field-Backofen equation, which extended the application of the simulation results.