A reader and method for adjusting the transmission time of a continuous wave (CW), wherein the method comprises setting an initial value for a response waiting time, sending the CW to a tag after sending a command to the tag and waiting for a response from the tag, judging whether the response from the tag is received within the response waiting time. If the response from the tag is received within the response waiting time, then sending of the CW is stopped and the response waiting time is adjusted. If the response from the tag is still not received beyond the response waiting time, then sending of the CW is stopped. The time for the reader to wait for a response from the tag is far less than 20 ms. Consequently, a command failure can be found early, so as to improve the processing efficiency of an RFID system.