An SPI-based data transmission system is provided. In the system, a master SPI apparatus enables a first slave SPI apparatus by using a combination of a first and a second chip select signal. In response to the master SPI apparatus driving the first chip select signal to be in an enable state and driving the second chip select signal to be in a disable state, the master SPI apparatus controls a second slave SPI apparatus to send data using a data line. The master SPI apparatus further receives data by using the data line, and the first slave SPI apparatus receives data using the data line. When the first chip select signal is in the enable state and the second chip select signal is in the disable state, the master SPI apparatus and the first slave SPI apparatus can simultaneously receive data transmitted by the second slave SPI apparatus.