For the structure limit of traditional wavelength scanning systems based on screw mandrel and step motor, they cannot simultaneously work both accurately and quickly. A new active opto-electrical feed-back measurement system based on laser, position sensitive detector and multilateral prism mirror is proposed in this paper. The grating is driven by a step motor directly and its rotational position is measured accurately by the active opto-electrical feed-back measurement system. The purpose of the new strategy is to make the wavelength scanning system work not only accurate but also quick. The elementary experimental results are satisfied.