A data storage device based on SPI includes an SPI circuit, a NAND flash memory for storing data, a NAND flash interface connected between the SPI interface and the NAND flash memory for controlling data transmission therebetween, an instruction controlling circuit connected between the SPI circuit and the NAND flash memory interface for converting an instruction received by the SPI circuit into an instruction recognizable to the NAND flash memory and a data converting circuit connected between the SPI circuit and the NAND flash memory interface for accomplishing conversion between serial data and parallel data. A data storage controlling method based on SPI is also disclosed. Thus a relatively small capacity and a relatively high price of a NOR flash memory based on SPI are avoided and costs are saved.