Nanoscale　defects　can　induce　the　effective　modulation　of　carrier　concentration,　mobility,　and　phonon　scattering　to　secure　high　thermoelectric　performance　in　semiconductors.　However,　it　is　still　limited　to　effectively　controlling　nanoscale　defects　in　thermoelectric　materials.　Here,　argon　plasma　bombardment　is　employed　to　introduce　a　large　number　of　point　defects　and　dislocations　in　microcrystalline　SnSe　powders,　synthesized　by　a　solvothermal　method.　After　sintering　these　powders　into　polycrystalline　bulk　materials,　bulk　SnSe　shows　the　ZT　increasing　by　up　to　66.7%　(from　0.36　to　0.6　at　773　K).　Through　detailed　micro/nanostructure　characterizations　and　first‐principles　calculations,　the　underlying　mechanism　is　elucidated　for　the　evaluation　of　thermoelectric　performance.　This　work　provides　a　deep　understanding　of　the　mechanism　of　nanoscale　defects　in　modulating　thermoelectric　performance　and　presents　experimental　evidence　and　experience　for　the　design　and　synthesis　of　efficient　thermoelectric　materials,　making　significant　contributions　to　future　green　energy　technologies.