The principle of competitive inhibition immunoassay is applied to the rapid test card of sodium pentachlorophenol. During the lateral movement of sodium pentachlorophenol in the sample, it binds to a specific monoclonal antibody labeled with colloidal gold, inhibiting the binding of the antibody to the sodium pentachlorophenol BSA conjugate on the NC membrane detection line, resulting in a change in the color of the detection line.