The aim of this work is to investigate conditions for the formation of Mo(VI)-VRT coordination compound. And reaction mechanism by spectrophotometric method. The method has been applied into the determination of trace molybdenum in samples of water form different sources, In the buffer solution of HAc-NH4Ac(pH=3.5), we can find that VRT and Mo(VI) form a stable binary complex. The apparent formation constant is 1.45×108, and we can also conclude that the method keep a linear relationship in the range of 0–14µg·mL−1, and give apparent molar absorptivity of 8.8×104L·mol−1·cm−1, This method is rapid, sensitive and convenient.