A method testing the quality of products applied to a system is provided. Each product includes a unique identification number. The system includes a data storage device and test devices. The data storage device includes a first table recording identification numbers, test types, and test results, each test device stores a second table records the identification numbers and the test types. The method includes: obtaining the identification number; obtaining the test type; determining whether a test type previous to the test type exists; and generating first information to prompt the operator to return the to-be-tested product to the workstation of previous test type when the test result corresponding to the existed previous test type does not exist or the test result corresponding to the existed previous test type is a first value.