The invention discloses an Al-Cr-Fe alloy coating on a stainless steel surface and a preparation method thereof. The coating comprises the following components: 27at.%-77.5at.% of Al, 16.5at.%-66at.% of Cr and 6at.%-20at.% of Fe. The preparation method comprises the following steps: step 1: chroming on the stainless steel surface; step 2: aluminizing on the chromium coating by a room-temperature fused salt aluminizing method, wherein the room-temperature fused salt for aluminizing is a system formed by AlCl3 and an organic salt which is one of alkyl pyridine halide, alkyl imidazole halide andalkali halide aryl ammonium salt; and step 3: thermally treating with the process parameters as follows: the temperature is 690-750 DEG C and the time is 1-16 hours. The Al-Cr-Fe alloy coating provided by the invention has high contents of aluminum and chromium and has excellent bonding force with a substrate, and the preparation method is suitable for parts in various shapes.