Abstract: A method for adjusting scanning speed of a scanner according to the data transmission rate between the scanner and a host computer to avoid accumulation of image data in the scanner's memory buffer is disclosed. The method comprises the following steps:(1) initiating a time counter and transmitting a test data packet from the scanner to the host computer;(2) acknowledging the scanner after the test data packet is completely received by the host computer;(3) stopping the time counter and calculating the time used for transmitting the test data packet;(4) calculating a data transmission rate according to the size of the test data packet and the time used to transmit the test data packet; and(5) adjusting the scanning speed of the scanner according to the data transmission rate.