The Internet of Things (IoT) is a technology trend that has been evolving in recent years. With the development of sensing technology and communication technology, the various applications of IoT are integrated into our lives gradually. Various security issues also need to be resolved with the convenience brought to us by IoT. MQTT or MQTT-SN is a lightweight communication protocol in IoT, which is more compactly on sensor nodes with limited resources. This paper provides a secure connection and end-to-end encrypted communication method which is based on MQTT-SN. By using digital signature (ECDSA), hash function, key exchange (ECDHE), AEAD (ChaCha20-Poly1305) to achieve a safe version of MQTT-SN called Safe MQTT-SN. The Safe MQTT-SN enables an end-to-end encrypted communication between the subscriber and publisher. The implementation of these algorithms enable the Safe MQTT-SN to have good performance on sensor nodes with limited computing power. Comparing with mosquito MQTT-TLS, the handshake time of MQTT-TLS is about 56.12ms and Safe MQTT-SN is about 24.78ms on Zedboard.