Thermogravimetric analysis experiments were carried out to investigate the pyrolysis properties of neutral sulfite semi-chemical pulp (NSSC) black liquor ranging from room temperature to 800 degrees C with heating rates of 20 degrees, 30 degrees, 50 degrees C/min. Experimental results show that the black liquor quickly loses weight in the temperature range of 170 degrees-370 degrees C, 370 degrees-570 degrees C, and 570 degrees-800 degrees C. The organic volatiles are mostly released in the former two ranges, while the alkali metal salts decompose, volatilize, and react in the third range. The mechanism function of NSSC black liquor pyrolysis is determined by means of the thermal analytic dynamics method and the most probable mechanism functions. The kinetic parameters for the chemical reactions were calculated by the Coats and Redfern method and the Ozawa method. Meanwhile, the pyrolysis dynamics equation of the NSSC black liquor is presented in this work. The results show that the activation energies of the NSSC black liquor decomposition calculated by the Ozawa method in the three temperature ranges are in general lower than that those calculated by the Coats and Redfern method.