An apparatus for monitoring beam currents of an implanter is provided. The apparatus includes a beam-sensing unit for sensing the beam currents; a position-determining unit for determining scan positions; and a computing unit. The computing unit is configured to perform the functions of receiving the beam currents from the beam-sensing unit; receiving the scan positions from the position-determining unit; and determining a drift status of the implanter from the beam currents, wherein the computing unit is configured to receive the beam currents and the scan position periodically between a starting time and an ending time of a scan process of the implanter.