With the continuous development of UAV technology. UAV Swarm receives increasing attention in some areas such as military. Due to the instability of battlefield, UAV is susceptible to hacking, and its data security gradually become a focus of research. Fine-grained access control and encryption can better secure the combat data, both of which can be accomplished by attribute-based encryption (ABE). However, the current ABE schemes are not suitable for UAV swarm in terms of efficiency and scalability. To improve the applicability of ABE schemes in UAV swarms, this paper proposes a scheme that combine ABE and scalar multiplication on elliptic curve with access tree innovatively utilized, which implements access control to combat data and improves the scalability. The efficiency of the proposed scheme is proven through the experiment and security analysis. Encryption time is less than 100 ms when the number of attributes is 100, which indicates proposed scheme is capable for more attributes. In addition, security analysis also show that the scheme is secure under chosen-plaintext attack and collusion attack.