An extensible millimeter wave security inspection system, a security inspection method for a human body using the extensible millimeter wave security inspection system and an extensible millimeter wave scanning unit are disclosed. The extensible millimeter wave security inspection system includes at least one security inspection passage, at least one scanning units are provided on at least one side of two sides of each security inspection passage, each scanning unit includes at least one millimeter wave transceiving module, the millimeter wave transceiving module includes an array of millimeter wave antennas configured to transmit and receive millimeter wave signals and a millimeter wave transceiver associated with the array of millimeter wave antennas, and the millimeter wave transceiving module is arranged to scan by millimeter wave a target to be inspected in the security inspection passage along a direction in which the security inspection passage extends.