Abstract: Diphenylcarbazide Spectrophotometry is a standard method to measure trace Cr (Ⅵ). However, using H₂SO₄ as the chromogenic medium has limitations such as a strict sulfuric acid concentration, short stability time of 10-60 min and poor sensitivity. An improvement was made to the diphenylcarbazide spectrophotometric method by replacing sulfuric acid with phosphoric acid as the chromogenic medium. Results indicate that the reaction is stable for 3 h in the phosphoric medium, and the detection limit is reduced from 13.6 μg/g to 3.8 μg/g with a recovery factor of 99.2%-102.0% and RSD≤5.25%. Compared with the routine method, the improved method, when applied to ultramafic rock standard materials demonstrates higher stabilization, precision and accuracy.