A resistivity measurement while drilling (MWD) device, including: a transmitting module arranged on an outer surface of a drill collar, for generating an induced current between the drill collar and surrounding formation by inductive coupling; a receiving electrode group including at least two electrodes, for receiving a measured current that reaches the electrode from the induced current through corresponding formation, two electrodes in the receiving electrode group being multiplexing electrodes; a resistivity calculation module configured to be connected to all or a part of the electrodes in the receiving electrode group in a measurement mode of the resistivity MWD device, to calculate the measured current received by a corresponding electrode and obtain resistivity of formation corresponding to the corresponding electrode; and a data transmission module configured to be connected to the multiplexing electrodes in a transmission mode of the resistivity MWD device, for transmitting calculated resistivity to a ground device.