The invention relates to a depth defense system for effectively responding to APT (Advanced Persistent Threat) attacks. The depth defense system comprises an Internet access area, a DMZ area, a core application area, a DB area, a data area, and a management area; the DMZ area is connected with the Internet access area; the core application area is connected with the Internet access area; the DB area is respectively connected with the DMZ area and the core application area; and the management area is respectively connected with the Internet access area, the DMZ area, the core application area and the DB area. The depth defense system provided by the invention adopts a deep network structure, which reduces the number of regional firewalls, reduces the equipment cost, shares the load to various hierarchical networks, realizes the function of releasing the pressure of a core switch, and improves the service life of the switch; besides, the division of functional modules is realized, and the controllability of each functional module is improved; and all functional sub-networks are of the closed loop design, and the security of the system is improved.