In order to measure the thickness of large-sized hollow rotating parts, a non-contact measuring method based on double laser displacement sensors was proposed. With unknown relative position between rotating parts and the double laser displacement sensor, the measuring errors induced by the installed eccentricity of rotating pieces as well as the non-collinear relationship between dual-sensor optic axis and the origin were analyzed. Meanwhile, mathematical model between dual-sensor signals and the thickness of the measured surface position was deduced. Thereby, the actual thickness value can be extracted from the sensor signals with the aids of the phase difference measurement based on correlation theory, Newton iterative method and the circulation translation method. Through the simulating experiment for the thickness detection algorithm of the rotary body, it is indicated that the relative detection error remains within 0.5% when the amplitude of the interference component in the detected signal is no greater than 0.3mm, which can be used as a reference for rotating speed adjustment of the turntable. The analysis on the experimental measurement data shows that the maximum relative translation of two detection signals is 4; with eccentricity compensation and cycle-spinning of the data, the measurement repeatability error of the thickness detection algorithm is less than 0.05 mm, which meets the detection precision requirement large-sized hollow rotating parts in any position.