A wireless network system and a connecting method thereof are provided. The wireless network system includes a Wi-Fi apparatus and a communication apparatus. The Wi-Fi apparatus provides a Service Set Identifier (SSID). The SSID includes a first identifier value and a second identifier value, and the second identifier value is derived from the first identifier value by a hash function. After searching the SSID of the Wi-Fi apparatus, the communication apparatus determines that a value derived from the first identifier value of the SSID by the hash function is equal to the second identifier value, and then establishes a Wi-Fi authenticating connection with the Wi-Fi apparatus according to a connection password. The Wi-Fi apparatus establishes a data transmission connection with the communication apparatus after determining that the communication apparatus is legal according to the Wi-Fi authenticating connection.