The invention discloses a method for detecting chemical residues, in particular to a method for detecting the residual amine content of a polyamide composite membrane piece. The method comprises the following steps that through a leaching-out process of the residual amine content of a reverse osmosis membrane piece, an alcohol water solution is adopted as an eluent; the content of the amine in theeluate is detected; and finally the residual amine content of the membrane piece is calculated. According to the method, a simple and efficient detection method combining residual amine leaching outand instrument testing is provided, the residual amine eluent dopts 20-100 wt% of the alcohol water solution, heating and soaking treatments are carried out for a certain time in the eluent through the membrane piece, the content of the amine in the eluate is detected by adopting an ultraviolet visible light-solar photometric method or a gas chromatography method, and then the content of residualamine in the membrane piece is converted; and the component of the eluate is simple, the preparation is convenient, the eluate is easy to detect, and the method is suitable for quantitative monitoringof the residual amine content of the reverse osmosis membrane.