Abstract: The effect of uniaxial stress field along <100> and <111> crystal direction on the diffusion of a single helium atom in bcc tungsten was studied by molecular dynamics simulation. Our calculation shows that the stress strain caused the phase transition of tungsten metal and the initio phase transition strain decreases with the increase of temperature. The initial strain of phase transition is near the strain where stress reaches the maximum value. The diffusion coefficient of a single helium atom in tungsten metal decreases with the increase of strain. The helium diffusion coefficient decreases linearly along the <100> crystal direction, while the <111> crystal direction shows a fluctuating trend. Fitting the Arrhenius equation, the results show that when the crystal strain along <100> reaches +1.5% and the Arrhenius equation is no longer applicable; however, the Arrhenius equation still applies when the crystal strain along <111> increases by +5%. The helium diffusion activation energy along the crystal direction <111> was obtained, the results showed that the helium diffusion activation energy decreases with the increase of strain, indicating that the strain enhanceds the mobility of a single helium atom in tungsten.