A rapid UV-Vis spectrophotometric method was proposed to determine the concentration of DMP in aqueous solutions. The linear concentration range of DMP solution at the range of 250～400 nm is 0.5～70 mmol·L(-1). At 275 nm, the linear fitting equation is A=0.030 7c+0.133 0 with a correlation of 0.980 9. The detection limitation is 9.46×10-5 mmol·L-1, the RSD (n=6) of the method were at the range of 0.100%～0.612%. The recovery ratio for salt solutions sample is 95%～104%. Temperature, pH, and coexisting K(+), Na(+), Mg(2+), Cl(-), Br(-), I(-), SO(2-)(4) ions do not affect the detection. The coexisting CO(2-)(3) and HCO(-)(3) ions can be eliminated with acidification. The results showed that the proposed method is simple in pretreatment process and has high accuracy and precision. It is a quick measurement method of DMP concentration in water solution, and can be used to measure DMP concentration in reverse flotation tail liquid and reverse flotation material pulp.