The invention provides a test system optimization method for simultaneously measuring the contents of copper, cobalt, nickel and iron in a zinc electrolyte. The method comprises: the amount of a colordeveloping agent is optimized; influences on the stability and sensitivity of the four kinds of trace ions by presence or absence of the sensitizer and the temperature change are examined; an optimalreaction temperature and the amount of the sensitizer are determined; according to an overlapping index of Fe<3+> and Fe<2+>, an available waveband range is determined; and then the feasibility of the test system optimization method is determined based on the linearity and additivity of the absorbance of copper, cobalt, nickel and iron. Under the optimized test system, the modeling experiments ofthe calibration set and the verification set are designed and completed; a partial least squares regression model is established by the calibration set; and the verification set is used for predicting the trace metal ion concentration of the to-be-tested zinc electrolytic solution. The test system has advantages of wide linearity, low detection limit, high selectivity and high sensitivity. The pre-separation of zinc electrolyte is avoided; the automation is realized easily; and simultaneous detection of various trace heavy metal ions in zinc electrolyte is realized.