1. A method for reading non-standard register of Serial Advanced Technology Attachment (SATA) devices by using an unused input parameter of a standard command to drive a SATA device to read a value of the non-standard register, and saving the value into an output register of the SATA device corresponding to an unused output parameter in response to the standard command, comprising the steps of: setting up the unused input parameter as an executive parameter; sending the standard command with the executive parameter into a SATA host controller for converting the standard command and the executive parameter to an input frame information structure; transmitting the input frame information structure to the SATA device for detecting the executive parameter by the SATA device to read the value of the non-standard register; and saving the value of the non-standard register into the output register of the SATA device.