The present invention relates to the field of product quality analysis, and specifically, a test kit and detection method for testing isothiazolinone in textiles. A pretreatment step of the present invention adopts a unique process, which may fully transfer isothiazolinone to an acetone and water mixed solution, so that a more accurate measurement result can be achieved. The testing method of the present invention dose not add indicators, does not use large-scale analysis instruments, and is accurate in measurement, easy in reaction termination determination, high in accuracy, low in cost, and strong in popularization and application.