The effect of alkaline thermal hydrolysis method on excess sludge and its characteristic parameters(such as soluble chemical oxygen demand, volatile fatty acids, ammonia-nitrogen, pH value, sludge concentration, etc.) were investigated. The results show that the addition of alkali can reduce the resistance of the sludge cells to high temperature and enhance the release and the hydrolysis of organic materials from the sludge cells with the increase of temperature, pH value and reaction time. The concentration of SCOD reached 17,950 mg/L and SCOD/TCOD was 0.65 on the conditions of pH 13, 170 degrees C and 75 min. The maximal dissolving rate of suspended solids (SS) was 67% and 72% for volatile suspended solids (VSS) at pH 13 with 60 min. The concentration of SCOD after alkaline thermal hydrolysis treatment increased with the increase of sludge concentration, in which the nice linear relation was reached and the correlation coefficient (R2) was above 0.97. The increasing rate of the SCOD was improving with the increase of the pH value and the SCOD of unit sludge reached 672 mg/g at pH 13. The effect of three factors on the SCOD was investigated through orthogonal experiment at the temperature of 170 degrees C, the importance was sludge concentration,pH value and reaction time in turn.