Electrochemical　reduction　of　CO2　into　renewable　carbon-neutral　fuels　has　been　extensively　studied.　Current　attentions　mainly　focus　on　the　development　of　high-performance　materials　and　molecular　dynamics,　fundamentals　on　kinetics　of　electrochemical　reduction　of　CO2　are　still　unclear.　Herein,　we　design　a　simplified　electrochemical　process,　CO2-saturated　K2SO4　solution　at　bismuth　electrodes,　to　elucidate　the　electrochemical　reaction　kinetics　of　CO2　reduction　reaction.　A　totally　irreversible　process　for　CO2　reduction　reaction　occurs　and　this　reaction　can　be　described　as　CO2　+　H2O　+　2e-　-＞　HCOO-　+　OH-.　It　is　firstly　reported　that　the　reduction　of　CO2　at　bismuth　electrodes　is　of　a　diffusion-controlled　process,　and　the　diffusion　coefficient　of　CO2　is　(1.98　+/-　0.22)　x　10-5　cm2　center　dot　s-1.　From　the　well-defined　linear　sweep　voltammograms,　electron　transfer　coefficient　is　obtained　as　0.18　+/-　0.01.　Combining　with　the　half-wave　potential　(-1.503　+/-　0.002　V　vs.　Ag/　AgCl　(sat.　KCl))　from　differential　pulse　voltametric　results,　the　standard　heterogeneous　rate　constant　is　estimated　to　be　(3.4　+/-　0.2)　x　10-3　cm　center　dot　s-1.　These　new　findings　may　identify　electrochemical　reaction　kinetic　questions　and　be　helpful　to　understanding　the　electrochemical　conversion　between　CO2　and　carbon-neutral　renewable　energy.