The rapid development of the Internet of Things further makes its data interaction vulnerable to various attacks.To ensure the security of data transmitted by UDP, the transport layer protocol of the Internet of Things, namely the DTLS (DatagramTLS) protocol, which supports the secure transmission of UDP datagrams, has been formed on the basis of the TLS protocol architecture.However, based on certificate public key cryptography, the existing DTLS protocol has disadvantages such as complex certificate management as well as high network communication overhead, thus cannot meet the secure communication requirements of resource-constrained networks such as the Internet of Things.Here, we propose an improved certificateless public key cryptographic scheme based on discrete logarithm, and design a lightweight DTLS protocol adaptable to resource-constrained networks, and then implement the protocol based on the embedded SSL library of wolfSSL.Finally, experiments are conducted to compare the DTLS protocol based on improved certificateless public key cryptography proposed in this article with the DTLS protocol based on traditional public key certificates and the DTLS protocol based on identity markers, and experimental results verify the superiority of the proposed protocol in terms of communication overhead and handshake delay.