Based on first-principles calculations, the electronic structures of Mn-doped SnTe via strain are investigated including spin-orbit coupling. Numerous results show that pristine SnTe exhibits narrow-gap semiconductor properties without magnetism, while Mn-doped SnTe system exhibits magnetic ground states dominated by 4d orbit of Mn atom with the doping concentration of 3.125% within the compression strain range (- 6% to 0). Interestingly, at the turning points of epsilon = -1% and -2%, a n-p-n-type transition can be observed. In addition, for the cases of epsilon = -1% and -2%, resonant states are introduced to the systems, which are beneficial to improving Seebeck coefficient in tailoring the thermoelectric properties. These results would provide a viable source on low-energy spintronic devices and pave the way to design n-type carriers adopted widely in thermoelectric materials.