The invention provides a method for measuring deviation quantity of strip steel at an air knife section in continuous strip steel hot galvanizing. A strip steel deviation quantity detector is arrangedon an operating side or a transmission side of the air knife section in continuous strip steel hot galvanizing and comprises a laser ranging sensor and a linear slider module. The laser ranging sensor is mounted above a supporting frame which is mounted above a slider of the linear slider module, the linear slider module is driven by a step motor or a servo motor, and the slider pulls the laser ranging sensor to reciprocate to measure strip steel positions in a moving process. By the high-precision laser ranging sensor, transverse and normal positions of the strip steel at the air knife section are detected, transverse deviation quantity and normal deviation quantity of the strip steel are calculated to make it convenient to timely adjust air knife and correction roller positions, and thickness uniformity of strip steel galvanizing layers is improved.