The invention provides a flash memory cell coupling ratio monitoring method. The method comprises a first step that a first test structure of a flash memory cell is manufactured, a second step that a test voltage is applied to a control grid electrode of the first test structure to obtain a first test result, a third step that a second test structure of the flash memory cell is manufactured, a fourth step that a test voltage is applied to a floating gate of the second test structure to obtain a second test result, and a fifth step that the first test result and the second test result are compared to determine whether a defect exists in an ONO structure of the flash memory cell.