Abstract: In order to solve the data integrality issue in the cloud computing, a new interactive integrality checking scheme is proposed. This scheme firstly constructs a perfect cartesian message authentication function type I and its equivalent function, then use synchronous verification value and the equivalent function to determine response message authentication value to detect integrity. Analysis results show that this new scheme can correctly check cloud file,s integrality with the difficulty of factoring large integer and only request constant computation, storage and constant network resource for the users, which is more computationally efficient than others.