A light-on module testing device, a method for testing a light-on module and a method for testing a display panel are disclosed. The light-on module testing device includes a base, a support element disposed on the base, and a test platform disposed on the base, wherein an arm is disposed on the support element, and the arm is configured to fix a light-on module to be tested, and a tester is disposed on the test platform and the tester has a signal output end.