Cloud computing is becoming one of the most convenient ways for information services through network accesses. In this paper, we describe the architecture of cloud computing and discuss the issue of in-cast, which may downgrade the transmission performance when the number of simultaneous transmission servers is getting larger. The in-cast transmission may introduce the out of sequence of packet delivery and may reduce the system throughput. This paper constructs the software environment to simulate the performance of video streaming services delivered by the servers in cloud. We first examine the performance of the out of sequence issue of packet transmission when the Hashed Credit Fair (HCF) algorithm was applied and investigate the multicast performance of video streaming service with respect to the numbers of servers. With the increasing of the number of servers, we note that transmission performance is not improved, on the contrary, the system throughput downgrades sharply. We believe the simulation results of this paper will be helpful for the design of cloud video multicast services.