Electrochemical　CO2　reduction　reaction　(CO2RR)　represents　a　sustainable　approach　to　alleviate　the　global　concern　associated　with　excessive　CO2　emission.　Recently,　metal-based　sulfides　are　emerged　as　a　special　class　of　electrocatalysts　for　efficient　formate　production,　which　however　suffer　from　massive　S　loss　during　CO2RR　due　to　the　compositional　reduction.　Herein,　we　synthesize　a　series　of　tin　sulfides　with　high　crystallinity　(i.e.,　SnS,　Sn2S3,　and　SnS2)　as　model　catalysts,　and　reveal　that　the　strength　distribution　of　Sn-S　bonds　in　atomic　configurations　is　essential　for　efficient　formate　production.　Typically,　the　strong　and　uniformly　distributed　Sn-S　bonds　in　SnS2　are　beneficial　for　inhibiting　S　leaching　and　forming　favorable　Sn/SnS2　heterointerfaces　for　CO2RR,　while　the　weaker　Sn-S　bonds　in　SnS　promote　the　reduction　into　metallic　Sn.　Specially,　the　Sn2S3　with　mixed　bonding　strengths　undergoes　consecutive　dissociation,　starting　from　cleaving　the　weakest　Sn-S　bonds　and　then　inducing　accelerative　reduction.　Resultantly,　the　SnS2　achieves　the　highest　Faraday　efficiency　of　93.8%+/-　0.59%　at　-1.0　V-RHE　and　a　high　partial　current　density　of　195.3　mA　cm(-2)　at　-1.2　V-RHE.　This　study　could　provide　insight　into　the　role　of　metal-sulfur　bonds　in　catalysts　for　efficient　CO2-to-formate　conversion.