The invention discloses a power-assisted bicycle using a sensor with position-adjustable magnetic blocks in a casing, which belongs to an electrically power-assisted bicycle for providing power-assisted signals through multi-point-position magnetic induction. The sensor comprises a sensing element, a power-assisted model processor, a D/A (digital to analog) converter and an operational amplifier which are sequentially connected, wherein the sensing element comprises permanent magnet blocks and a hall arranged in an inner cavity formed by that a movable plate and a fixed plate are mutually embedded, the movable plate is provided with a plurality of permanent magnet blocks, wherein two adjacent permanent magnet blocks are opposite in magnetic polarity, and the distance between the permanent magnet blocks can be adjusted, and the hall on the fixed plate is arranged at a position close to the permanent magnet blocks. The sensor is sleeved outside of a middle axle of the bicycle, and the operational amplifier is connected with a motor controller. The power-assisted bicycle disclosed by the invention has the advantages that: the relative positions between the permanent magnet blocks and the hall are fixed, and the hall can acquire rectangular wave signals, thereby facilitating that the sensor outputs reasonable forces (which are artificially set and can be adjusted) from the power-assisted model to a power-assisted starting point and a power-assisted ending point through digital processing, so that the man-machine cooperation can be optimal, and an effect of power saving can be achieved.