1. A method of controlling the loading status of a DLL in a streaming program, said method comprising the steps of: calling, by an operation module in said streaming program, said DLL during the execution of said streaming program; receiving, by a receiving unit, a triggering signal identifying a stream branch; determining, by a determining unit, an unnecessary operation module which corresponds to said stream branch by referring to an association table; and unloading, by an unloading unit, a DLL called by said unnecessary operation module thereby freeing at least a portion of a system's memory.