In order to improve the efficiency of a vegetable waste fermentation system and promote its stable operation under high organic load,the continuous anaerobic fermentation experiment of vegetable waste was carried out under the high temperature of 55 ℃. The indexes of early warning for instability of the anaerobic fermentation system were determined. The results showed that the instability early warning performance of bicarbonate alkalinity (BA) was strongest, and its early warning could be given 23 days in advance. When the concentration of BA was less than 1 500 mg/L, the system showed signs of instability. The early warning of acetic acid and n-butyric acid was given 22 days and 21 days in advance,respectively. CH4/CO2 could give early warning 21 days in advance. When CH4/CO2<1.23, acidification appeared in the system. The total volatile fatty acid/bicarbonate alkalinity (VFA/BA), bicarbonate alkalinity/total alkalinity (BA/TA) and intermediate alkalinity/bicarbonate alkalinity (IA/BA) could give early waring 16 days in advance. The critical values of early waring were VFA/BA>1.8, BA/TA<0.5, and lA/BA>1.2, respectively. The early warning performance of pH and oxidation reduction potential (ORP) was poor ,and their warning days were less than 10 days.