The invention discloses a preparing method for EXP-3174. The preparing method is characterized in that losartan is used as a starting raw material and is prepared into EXP-3174 through two-step oxidation. The preparing method has the greatest advantages that a reaction is moderate, the number of side reactions is small, aftertreatment is simple, and EXP-3174 with the purity of 99.9% can be obtained without column chromatography isolation.