An extensible millimeter wave security inspection system comprising: at least two security inspection passages (600, 610, 620) each provided with at least one scanning unit (100, 200, 300) at at least one side of two sides thereof, each scanning unit (100, 200, 300) comprising at least one millimeter wave transceiving module (10, 10'), and wherein the millimeter wave transceiving module (10, 10') comprises 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 (10, 10') is arranged to scan, by millimeter wave, a target to be inspected in the security inspection passage (600, 610, 620) along a direction in which the security inspection passage extends (600, 610, 620), wherein the at least two security inspection passages comprise a first security inspection passage and a second security inspection passage adjacent to each other, and wherein the at least one scanning unit (100, 200, 300) comprises a common scanning unit (200, 300) which is provided between the first security inspection passage and the second security inspection passage to separate the first security inspection passage from the second security inspection passage, the common scanning unit (200, 300) having one scanning operation surface on which the millimeter wave transceiving module (10, 10') is arranged facing towards the first security inspection passage and another scanning operation surface on which another millimeter wave transceiving module (10, 10') is arranged facing towards the second security inspection passage, wherein each scanning unit (100, 200, 300) comprises: a first linear transmission device and a second linear transmission device, and wherein the millimeter wave transceiving module (10, 10') is slidably connected to the first linear transmission device and the second linear transmission device, the first linear transmission device and the second linear transmission device being arranged to drive the millimeter wave transceiving module (10, 10') to move along the direction in which the security inspection passage (600, 610, 620) extends to achieve scanning operation. at least two security inspection passages (600, 610, 620) each provided with at least one scanning unit (100, 200, 300) at at least one side of two sides thereof, each scanning unit (100, 200, 300) comprising at least one millimeter wave transceiving module (10, 10'), and wherein the millimeter wave transceiving module (10, 10') comprises 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 (10, 10') is arranged to scan, by millimeter wave, a target to be inspected in the security inspection passage (600, 610, 620) along a direction in which the security inspection passage extends (600, 610, 620), wherein the at least two security inspection passages comprise a first security inspection passage and a second security inspection passage adjacent to each other, and wherein the at least one scanning unit (100, 200, 300) comprises a common scanning unit (200, 300) which is provided between the first security inspection passage and the second security inspection passage to separate the first security inspection passage from the second security inspection passage, the common scanning unit (200, 300) having one scanning operation surface on which the millimeter wave transceiving module (10, 10') is arranged facing towards the first security inspection passage and another scanning operation surface on which another millimeter wave transceiving module (10, 10') is arranged facing towards the second security inspection passage, wherein each scanning unit (100, 200, 300) comprises: a first linear transmission device and a second linear transmission device, and wherein the millimeter wave transceiving module (10, 10') is slidably connected to the first linear transmission device and the second linear transmission device, the first linear transmission device and the second linear transmission device being arranged to drive the millimeter wave transceiving module (10, 10') to move along the direction in which the security inspection passage (600, 610, 620) extends to achieve scanning operation. a first linear transmission device and a second linear transmission device, and wherein the millimeter wave transceiving module (10, 10') is slidably connected to the first linear transmission device and the second linear transmission device, the first linear transmission device and the second linear transmission device being arranged to drive the millimeter wave transceiving module (10, 10') to move along the direction in which the security inspection passage (600, 610, 620) extends to achieve scanning operation.