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: the host interface utilized to transmit a writing data queue of an up-layer application; the controller utilized to receive a writing data command queue from the host interface, to control devices such as 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 module of the writing data command queue from the controller, and adopts a direct writing or a cache writing for writing a current-requesting writing data; and based on a determination result, the cache and direct writing determination module directly writes the data which needs direct writing to the storage medium through the data writing channel, and writes the data which needs cache writing to the storage medium after it is cached by the cache module.