With the growth of Internet video traffic and the improvement of user requirements for experience quality， the traditional backbone network is facing great pressure. Moving edge cache technology can reduce latency， reduce backhaul link load， and improve video user experience quality. However， the finiteness of edge server cache resources， the dynamic nature of video requests， and the attention of users to the security of cached data pose new challenges to the research of edge cache strategy. To solve the above problems， this paper proposes a blockchain-assisted multi-edge server collaborative video stream cache optimization scheme. This paper constructs a four-layer network architecture composed of content delivery network （CDN） server， edge server， user device， and blockchain. We introduce the blockchain consensus mechanism to protect the charging video with insensitive request delay and ensure the data security of users. Based on the three-layer cache mechanism of local hit， proximity hit and CDN hit， the collaborative cache among edge servers is further strengthened by defining proximity hit reward factors， and the cache hit ratio of edge servers is improved. In this paper， we jointly consider the state of edge servers， the change in content popularity， and the resource allocation of cooperative cache among multi-edge servers. By establishing the minimum access latency， traffic cost， and system energy consumption optimization problem. The cooperative cache optimization algorithm of multi-agent proximal policy optimization （MAPPO） is used to solve the problem. The simulation results show that compared with the existing caching strategies， the proposed scheme can effectively improve the cache hit rate of video streaming and reduce energy consumption and delay.