The invention discloses an online test device and method of an integrated circuit. The test device comprises a single-chip microcomputer, an address decoding circuit, a data caching circuit, a test driving circuit, a relay device interface circuit, a voltage comparison circuit, a sampling circuit and a threshold circuit; an instant heavy current is input into or output from the input level of a tested device, so that the potential is increased or decreased according to requirements, test output response of the tested device is collected and compared, and fault information and fault position of the tested device are determined. Online test for components in the integrated circuit is realized, test is intelligent and efficient, the measuring accuracy is high, the integrated circuit is avoided from damage in the dismounting process of offline test, problems, as weakening of a current driving capability, which cannot be tested unless in the power-on state of the components of the integrate circuit can be tested, test functions are more comprehensive, and the testing efficiency and performance of the integrated circuit are further improved.