Abstract: A bill position adjustment method and system for bill acceptor is disclosed to include a body with an insertion slot and a bill passage, a transmission mechanism for transferring an inserted bill, a recognition device for recognizing the authenticity and value of an inserted bill, an entrance sensor and a stoppage sensor mounted in the bill passage for controlling the transmission mechanism to transfer the inserted bill into position for recognition, a bill passage adjustment mechanism for adjusting the width of the bill passage to correct the direction of an inserted bill into accurate alignment with the recognition device, and a bill sensor mounted in a sensor zone in the insertion slot for detecting the width of an inserted bill and controlling the bill passage adjustment mechanism to adjust the width of the bill passage subject to the detection result.