In order to solve the problems about decentralized electronic evidence, low efficiency of forensic analysis, cooperative forensics difficultly, etc. A collaborative digital forensics model with positive feedback loop mechanism based on cloud computing are designed according to the needs of digital discovery and analyze cooperatively, which is based on the characteristics of the computer crime and related problems of the current digital forensics. Then, design idea and architecture of the model are discussed in detail. Finally, the realization method and key techniques of the model are analyzed, such as scheduling policy for cloud storage and task scheduling for electronic evidence based on locking mechanism. Experiments show that collaborative digital forensics could effectively improve the efficiency of digital forensics and the accuracy of analysis results.