The present invention provides a decentralized coded caching placement method and system for files with heterogeneous sizes. The method uses a decentralized coded caching optimization placement method, in combination with the size of files at a server, the capacity limit of the local cache of user terminals and file downloading requests of different user terminals, to determine the cache proportions of files to be cached by user terminals, finally realizing the minimization of the code rate required by a shared link at the server for satisfying various file downloading requests of user terminals. The present invention improves the utilization rate of the local cache of user terminals, and effectively reduces the load of the shared link at the server.