A data transmitting method for a memory storage apparatus is provided. The method includes: initially setting a first threshold and a first accumulated value; and updating the first threshold by using the first threshold plus the first accumulated value at intervals of a first predetermined time. The method also includes when a detected temperature of the memory storage apparatus is greater than or equal to a temperature threshold, determining whether a size of received writing data is greater than or equal to the first threshold; and if no, writing the writing data into a rewritable non-volatile memory module and then updating the first threshold by using the first threshold minus the size of the writing data; and if yes, not writing the writing data into the rewritable non-volatile memory module. Accordingly, the method can effectively prevent overheat of system during operations of the memory storage apparatus.