This paper analyzes the simultaneous measurement method for the higher content soluble heavy metal elements of Cd2+, Cu2+, Zn2+, and Ni2+ which are heavy pollution in coastal and river water, demonstrates the properties of corresponding characteristic spectrum and absorbance of the four elements, establishes the mathematical model to function the concentration and total absorbance at the characteristic wavelength when the four elements dependent each other. We focus on effects of different situation of pH, temperature, time chromogenic dose on the metal ion concentration simultaneous measurement and summarize the experimental law.