To study the effect of strain engineering on the thermoelectric properties of SnSe, we combined first-principles calculation and Boltzmann transport theory to study the effect of −4% to 4% strain on SnSe thermoelectric properties. Compressive strain enhances the maximum power factor (PF_max) of p-type SnSe from 2.3 to 4.3 mW·m⁻¹·K⁻². Specifically, under a −3% compressive strain, the thermoelectric figure of merit (ZT) experiences a 50% enhancement, increasing from 0.18 to 0.27. Conversely, for n-type, tensile strain leads to a 26% rise in the PFₘₐₓ, from 53.6 to 67.6 mW·m⁻¹·K⁻². Notably, the 4% tensile strain increased the ZT value of n-type SnSe by 123% from 0.66 to 1.47. Importantly, tensile strain effectively reduces lattice thermal conductivity through enhanced phonon scattering, synergistically improving ZT with the enhanced power factor. The results show that strain can effectively improve the thermoelectric properties of SnSe, and that n-type SnSe has great potential in thermoelectric materials.