1. A dynamic caching system for a data storage system, comprising a host interface, a controller, a cache and direct writing determination module, a cache module, a data writing channel, and a storage medium, wherein: the host interface utilized to transmit a writing data command queue of an up-layer application; the controller utilized to receive the writing data command queue from the host interface, to control devices comprising the cache and direct writing determination module, the cache module, the data writing channel, and to write data to the storage medium; which is characterized by: the cache and direct writing determination module performs a real-time determination for a corresponding data blocks of the writing data command queue from the controller, and adopts a direct writing or a cache writing for writing the corresponding data blocks; and based on a determination result, the cache and direct writing determination module directly writes the corresponding data blocks which are direct writing to the storage medium through the data writing channel, or writes the corresponding data blocks which are writing to the storage medium after they are cached by the cache module, wherein adoption of the data writing or the cache writing is determined by an upper limit Tbuf of a length of the cached corresponding data blocks which is dynamically auto-adaptive.