As a leading contender to replace lead halide perovskites, tin-based perovskites have demonstrated ever increasing performance in solar cells and light-emitting diodes (LEDs). They tend to be processed with dimethyl sulfoxide (DMSO) solvent, which has been identified as a major contributor to the Sn(II) oxidation during film fabrication, posing a challenge to the further improvement of Sn-based perovskites. Herein, we use NMR spectroscopy to investigate the kinetics of the oxidation of SnI2, revealing that autoamplification takes place, accelerating the oxidation as the reaction progresses. We propose a mechanism consistent with these observations involving water participation and HI generation. Building upon these insights, we have developed low-temperature Sn-based perovskite LEDs (PeLEDs) processed at 60 °C, achieving enhanced external quantum efficiencies (EQEs). Our research underscores the substantial potential of low-temperature DMSO solvent processes and DMSO-free solvent systems for fabricating oxidation-free Sn-based perovskites, shaping the future direction in processing Sn-containing perovskite materials and optoelectronic devices.