In order to ensure the communication security of users and improve the high latency of traditional solutions in the integrated network of space and ground. In this paper, we propose a lightweight certificateless key agreement scheme. Firstly, we analyze the certificateless key agreement protocol system model. Based on the characteristics of the integrated network of space and ground, it is proposed that the protocol needs to satisfy some security requirements such as two-way authentication, anti-replay, and integrity. Then, we choose a lightweight certificateless encryption scheme. Base on the encryption scheme, we propose a key agreement protocol to meet the resource and security requirements of the integrated network of space and earth. Finally, we prove the proposed key agreement protocol security conducted on the BAN logical analysis, and compare the protocol performance with software simulation. The results show that the solution not only meets the network security requirements, but also provides fast and efficient negotiation.