The invention provides an electrochemical water treatment device. The device includes a baffle plate, screws, water collecting and distributing grooves, a multi-stage channel electrode waterproof insulation pad, a multi-stage channel electrode terminal, a bearing plate, a device shell cover, a counter electrode terminal, a counter electrode, a device shell, a multi-stage channel electrode, a counter electrode waterproof insulation pad, a sealing gasket and communicating pipes; the multi-stage channel electrode has a micron channel parallel to the surface of the multi-stage channel electrode, and a nanochannel vertical to the surface of the multi-stage channel electrode, and a to-be-treated water pathway exists between two poles; the micron channel parallel to the surface of the multi-stagechannel electrode is an oxygen-containing gas pathway; and gas and liquid phases are in contact with each other to perform reaction through the nanochannel vertical to the surface of the multi-stagechannel electrode. The gas and liquid phases are reacted with each other in nano space at the internal of the multi-stage channel electrode, and the limitation of charge transmission and substance transmission can be broken through, so that water treatment efficiency can be significantly enhanced; and the device is simple in structure, low in cost, small in energy consumption and land occupation and long in service life, and used for various wastewater treatment.