A method, a device and a system for running an application are disclosed. The method includes: creating a process corresponding to the application, and loading pre-generated data file description information of the application (101); monitoring I/O requests of the application through the process, and when an I/O request of the application is monitored, determining a type of a file to be accessed by the application according to the I/O request (102); if the type of the file to be accessed by the application is a data file, acquiring data blocks required by the application from a server side according to the data file description information (103); loading the data blocks into a memory (104). The technical solution can simply and efficiently decrease the installation package size of an application without special customization.