A liquid particle counter was developed with electrical resistance method and a method of detecting heavy metal Cu²⁺ combined with the click chemistry method to solve the problems including the complicated operation，long cycle of detection and high cost of detection existed in the current methods of detecting heavy metals in water quality. A model for identifying the particle size and a model for particle counting were established. A particle counting software based on LabVIEW was developed. A rapid method of detecting Cu²⁺ in water was realized by using polystyrene microspheres as detection probes and particle counters as detection platforms. The results showed that the relative error of particle size identification and particle counting was less than 5% and 10%，indicating that the accuracy of particle counting meets the requirements. When the concentration of Cu²⁺ was 10-1 000 μmol/L，there was a good linear correlation between the number of polystyrene microspheres and the concentration of Cu²⁺. The average recovery rate was between 87.85% and 101.08%. The detection limit was 2.29 μmol/L. The time of detection was about 4 min. Compared with the traditional method of detecting Cu²⁺，the method of detecting Cu²⁺ with a liquid particle counter based on the electrical resistance method has the advantages of simple operation，fast speed of detection，high sensitivity and low cost of detection.