Current density distribution is a crucial parameter in plasma physics, which plays an important role in plasma simulation, advanced operation mode development, current drive, confinement, and transport. The stark spectrum caused by injecting a neutral beam into plasma contains σ component, and π component. When viewed transversely to the electric field, the polarization direction of the σ component is perpendicular to the direction of the equivalent electric field, and the polarization direction of π component is parallel to the equivalent electric field, the distribution of current plasma density can be deduced by measuring polarization direction of the splitting spectrum.The polarization detection system based on a dual photoelastic modulator system has the unique advantages of high detection accuracy and quick time response, which is very suitable for measuring current density distribution under the rapid variation of plasma current. An external driving source causes the elastic deformation of birefringent crystals, and the refractive index changes periodically, then the modulated light intensity changes are formed through the polarizer. The polarization detection system of MSE diagnostic consists of two Photoelastic Modulators (PEM) and a polarizer. By detecting the ratio of modulation intensities at different modulation frequencies, the polarization direction of the splitting spectrum can be obtained quickly and accurately, and then the plasma current density distribution can be obtained. This paper introduces the polarization detection system of MSE diagnosis on Experimental Advanced Superconducting Tokamak (EAST), The off-line test and calibration of the system were completed, and the preliminary result of plasma current density distribution was obtained in experiments.