At present, the smart home system based on wireless technology has brought comfort and convenience to people, but the system is vulnerable to attack, and there are more private data to be protected. For the data security problem in wireless communication, a kind of smart home system and its secure communication method is designed, namely, the networking structure of the system is designed, external network and internal network are planned. The home device nodes in internal collect information and apply ZigBee to communicate mode, while other devices apply WiFi to communicate. The router is deployed as MQTT server, mobile phones and other control devices are MQTT clients, and SSL communication is configured on server, client program is designed. While the MQTT client in the external network accesses the server, it uses first secure intranet penetration scheme of Zerotier to connect to the internal network, and then generates public keys and certificates by SSL protocol for secure communication. The cross diffusions method of L-P chaotic system is proposed to generate AES initial round key, and applied to ZigBee secure communication. The experimental results are that MQTT client in internet and server can connect to a ZeroTier network and communicate securely through SSL protocol can communicate securely; ZigBee communication mode achieves the encryption effect, compared with the standard AES algorithm, it is shorter encryption time and shorter communication delay, which are reduced by 3.77%, and 28.5% respectively, and less energy consumption, the average residual energy of nodes is increased by 30.22%. Therefore, the experimental results show that the communication method proposed in this paper is secure and applicable.