Trust has attracted extensive attention in social science and computer science as a solution to enhance the security of the system. This paper proposes a trust evaluation model based on D-S evidence theory and sliding windows for cloud computing. The timeliness of the interaction evidence as the first-hand evidence is reflected by introducing sliding windows. The direct trust of entities is computed based on the interaction evidence by D-S evidence theory. The conflict of the recommendation trust as the second-hand evidence is eliminated with a help of an improved fusion approach as far as possible. Finally, the combination of the recommendation trust exposes the credibility of entities. Experimental results show that the proposed model is effective and extensible.