A data transmitting method, a memory storage device and a memory control circuit unit are provided. The method is used for a data transmitting operation between the memory storage device and a host system. The host system is recorded with a plurality of submission queues, and the method includes: obtaining at least one first command in a first submission queue from the host system and determining whether a first data quantity of the at least one first command matches a first predetermined condition; obtaining at least one second command in a second submission queue from the host system if the first data quantity matches the first predetermined condition; and sequentially performing a data accessing operation corresponding to the at least one first command and the at least one second command on a rewritable non-volatile memory module in the memory storage device.