Brownian motion of 2D nanorods can be described by translational diffusion and rotational diffusion. In this paper, a method called depolarized-polarized image-based dynamic light scattering (DIDLS) is proposed, which is used for measuring the size and size distribution of nanorods by analyzing the vertical-vertical and vertical-horizontal polarized dynamic light scattering signals induced by the translational and rotational diffusions of nanorods with Brownian movement under polarized laser. Firstly, the correlation degree function between consecutive polarized dynamic images is studied, and the average values of the translational and rotational diffusion coefficients can be estimated. Then, the length as well as ratio of length to diameter of nanorods are calculated through two inversions, and the two-dimensional distribution of particles is obtained. The influence of laser wavelength on measurement results is analyzed, and the baseline value is suggested as a criterion for judging the signal and noise ratio (SNR). The measurements for gold nanorods with diameter of 20 nm and length of 300 nm under 650,780,and 905 nm laser wavelengths are conducted, and the average size and size distribution of gold nanorods are obtained.