The invention provides a deep packet inspection method, device and system for a cloud terminal Wi-fi system. The deep packet inspection method comprises the steps that after authentication of a user terminal connected with an access point (AP) is accomplished by a cloud access controller (AC), a notice shows that the user terminal passes authentication and is issued to the AP, and a deep packet inspection identification is carried by the notice so that the AP can continue uploading packets of the user terminal; the cloud AC receives a package of a current data stream of the user terminal through the AP; the cloud AC conducts deep packet inspection on the package of the data stream through a package inspection device, wherein the package inspection device is arranged on the AC or independently arranged on a cloud terminal; after the cloud AC determines that deep packet inspection of the data stream is accomplished by the package inspection device, the AP is instructed to process the data stream in a local forwarding mode. By the adoption of the deep packet inspection method, device and system for the cloud terminal Wi-fi system, the problem that a deep packet inspection (DPI) technology cannot be effectively implemented by an existing cloud terminal Wi-fi system is solved, and performance of the system is improved.