An interface integrated circuit for vehicle diagnosis/programming and a vehicle diagnostic instrument comprising the interface integrated circuit, and a communication method for transmitting data between a microprocessor and an on-board diagnostic system via the interface integrated circuit, and a corresponding communication system. An interface integrated circuit (200) comprises: a communication control unit (110) comprising a plurality of communication protocol core modules, wherein each communication protocol core module performs signal conversion according to a communication protocol and each communication protocol core module can switch between a vehicle condition query and parameter setting mode and a vehicle condition acquisition mode; and a port drive unit (120) comprising a plurality of drivers, wherein each of the plurality of drivers comprises a plurality of drive modules, and the plurality of drive modules are correspondingly connected to the corresponding communication protocol core modules in the communication control unit (110) and appropriately convert a signal level so as to meet signal level requirements of different communication protocols, so that a random combination of the transceiving of signals of a plurality of communication protocols can be obtained so as to be flexibly suitable for a plurality of vehicle models.