Owing to the wind resistance and excellent weld bead performance of self-shielded flux cored wire. It has been widely used in pipeline welding and the repair of large machinery in the field. Especially, electrode polarity has a great effect on the welding process. In order to study the influence mechanism of electrode polarity on arc plasma, a synchronous acquisition system was designed to scan each point in arc plasma space. Through the analysis of characteristic spectra lines, the Stark profile method was used to calculate the electron density, and the arc plasma temperature was calculated based on the Boltzmann mapping method. At the same time, the distribution characteristics of Al and Mg active elements were analyzed. The results show that electron density distribution, arc plasma temperature and active elements in the central area of the arc column were like the water drop along the negative direction of the Y axis in DCEN (direct current electrode negative). Under the DCEP (direct current electrode positive), the distribution characteristics of arc plasma electron density, arc temperature and active elements in the central area of the arc column were fingerlike. According to the principle of self-magnetic contraction, the electromagnetic force was less in the radial direction under DCEP, and the distribution of active elements was divergent. Under DCEP, the active elements are subjected to more electromagnetic force in the radial direction, and the shrinkage was serious. In addition, the arc plasma electron density and arc temperature in the center of the arc column were higher in DCEP than those under DCEN when the same electrical parameters were used. The distribution characteristics of electron density and ionization degree were the main factors affecting the arc plasma temperature. The arc plasma temperature and electron density were raised with the current and voltage increase under the same electrode polarity.