A caching system applied to a network, comprising a caching policy control device and at least one main cache device, characterized in that: the caching policy control device is configured to receive a content caching request sent by an external packet data network, PDN, and control, according to the content caching request, the at least one main cache device to cache external content, wherein the external content is content sent by the external PDN; and the at least one main cache device is connected to the caching policy control device, and is located on a data channel between an anchor gateway of the network and the external PDN, and configured to cache the external content according to the control of the caching policy control device; wherein the caching policy control device comprises: a request acquiring module, configured to receive the content caching request sent by the external PDN; a permission determining module, configured to determine, according to the content caching request and a predetermined caching policy, whether to allow the at least one main cache device to cache the external content; and a caching control module, configured to, when a determination result of the permission determining module is that caching is allowed, send a main-cache command to the at least one main cache device, to control the at least one main cache device to cache the external content; wherein the at least one main cache device comprises: a main-cache starting module, configured to receive the main-cache command sent by the caching policy control device, and allocate local storage space according to the main-cache command; a main-cache notification sending module, configured to notify the caching policy control device after the local storage space is successfully allocated, so that the caching policy control device notifies the external PDN to send the external content to the main cache device; and an external-content receiving module, configured to receive the external content sent by the PDN. the caching policy control device is configured to receive a content caching request sent by an external packet data network, PDN, and control, according to the content caching request, the at least one main cache device to cache external content, wherein the external content is content sent by the external PDN; and the at least one main cache device is connected to the caching policy control device, and is located on a data channel between an anchor gateway of the network and the external PDN, and configured to cache the external content according to the control of the caching policy control device; wherein the caching policy control device comprises: a request acquiring module, configured to receive the content caching request sent by the external PDN; a permission determining module, configured to determine, according to the content caching request and a predetermined caching policy, whether to allow the at least one main cache device to cache the external content; and a caching control module, configured to, when a determination result of the permission determining module is that caching is allowed, send a main-cache command to the at least one main cache device, to control the at least one main cache device to cache the external content; a request acquiring module, configured to receive the content caching request sent by the external PDN; a permission determining module, configured to determine, according to the content caching request and a predetermined caching policy, whether to allow the at least one main cache device to cache the external content; and a caching control module, configured to, when a determination result of the permission determining module is that caching is allowed, send a main-cache command to the at least one main cache device, to control the at least one main cache device to cache the external content; wherein the at least one main cache device comprises: a main-cache starting module, configured to receive the main-cache command sent by the caching policy control device, and allocate local storage space according to the main-cache command; a main-cache notification sending module, configured to notify the caching policy control device after the local storage space is successfully allocated, so that the caching policy control device notifies the external PDN to send the external content to the main cache device; and an external-content receiving module, configured to receive the external content sent by the PDN. a main-cache starting module, configured to receive the main-cache command sent by the caching policy control device, and allocate local storage space according to the main-cache command; a main-cache notification sending module, configured to notify the caching policy control device after the local storage space is successfully allocated, so that the caching policy control device notifies the external PDN to send the external content to the main cache device; and an external-content receiving module, configured to receive the external content sent by the PDN.