A test layout, a system, and a method for detecting leakage current are disclosed. The test layout module includes M PN junction diode leakage current test units formed in the FEOL process, parallel-connect with a classical leakage current test unit formed in the metal layer; wherein, P-regions of the PN junction diodes are connected to a high potential, N-regions of the PN junction diodes are connected to a low potential, the junction areas of the PN junction diodes are different each other, each of the PN junction diode leakage current test units is controlled by one switch respectively, the positive integer M is greater than or equal to 1. Through paralleling the PN junction diodes formed in the FEOL process with the classical leakage current test unit in the metal layer, not only the required test layout area utilized to detect the leakage current in the metal layer is reduced, but also the detecting accuracy is further enhanced.