The invention discloses an equipment access sensing method based on an ARP protocol. The method comprises the following steps: blocking an ARP broadcasting function and a response function of a self operating system; constructing a private ARP request message, wherein the private ARP request message is a message which increases a corresponding private mark with a signature based on an original ARP request message; broadcasting the private ARP request message, at the same time, receiving the private ARP request messages transmitted by other host equipment, and returning a private ARP response message; detecting whether the private ARP request messages transmitted by the other host equipment contain the private mark with the signature or not; if the private ARP request messages transmitted by the other host equipment contain the private mark with the signature and the signature is right, judging the other host equipment as legitimate access equipment, and performing normal communication, and if not, judging the other host equipment as illegal access equipment, and blocking the communication of the illegal access equipment; reporting the information of the illegal access equipment to a server. Through the adoption of the method disclosed by the invention, the equipment access can be quickly and timely found, and the communication of the illegal access equipment is effectively stopped.