The invention provides a differential type high-precision liquid level detection method used for quantitative concentration, and belongs to the field of tests. A first liquid level detection sensor and a second liquid level detection sensor are arranged to form a differential type double-sensor set. The position of the to-be-detected liquid level in a constant-volume pipe is detected according to the light refraction principle. The transmitting terminals and the receiving terminals of the first liquid level detection sensor and the second liquid level detection sensor are all arranged on a sensor supporting plate. The sensor supporting plate is fixedly connected to a lifting mechanism used for driving the sensor supporting plate to move up and down in the longitudinal direction. Different liquid levels in the constant-volume pipe are detected through the vertical movement of the first liquid level detection sensor and the second liquid level detection sensor. According to the technical scheme, the position of the to-be-detected liquid levels in the constant-volume pipe is detected through the differential type double-sensor set, and therefore the problem that the detection accuracy of the transparent liquid level detection sensors is low when the light emitting beam is large is solved, and the small-volume and high-precision constant-volume detection operation is achieved. The differential type high-precision liquid level detection method is suitable for the field of high-precision liquid level detection in the quantitative condensation process in pretreatment of chemical samples.