A suspicious packet detection device and a suspicious packet detection method thereof are provided. The suspicious packet detection device captures an HTTP packet transmitted from an internal network to an external network, and based on an HTTP header of the HTTP packet, determines that the HTTP packet belongs to one of a browser category and an application category and identifies the HTTP packet as one of a normal packet and a suspicious packet. When the HTTP packet is identified as the normal packet, the suspicious packet detection device further verifies whether the HTTP packet is the suspicious packet or not by comparing the HTTP header with relevance information or by using a URL classification model.