Abstract: The paper present a new spectrophotometric method for the determination of trace Hg(Ⅱ), in polyvinyl alcohol solution thiocyanate and butyl rhodamine B produce multi-ionic associated substance with Hg(Ⅱ).it is at 580nm that absorption of the ion association complex is the maximum, Beer′s law is obeyed in the range of Hg(Ⅱ)0~6 μg/25mL.The molar absorptivity is 7.08 ×10⁵L·mol^-1·cm^-1.Through the determination of Hg(Ⅱ)in battery and water, the result shows that the reaction system can tolerate many interfering ions due to the existence of polyvinyl alcohol.Only iron(Ⅲ) and zinc(Ⅱ)interfere in the determination of Hg(Ⅱ), and it can be eliminated by masking with ascorbic acid(5%)and lemon acid(10%).The recommended method is characterized by its simple operation、fast speed、strong selectivity and good reproductive.