The start-up time of an ANAMMOX reactor can be shortened when it is inoculated with ANAMMOX sludge, so it is necessary to develop a cost-effective preservation technique for the sludge. The flocculent ANAMMOX sludge was preserved at 30°C, natural environment, 5°C and -20°C for 15d, 30d, 45d, 150d and 365d, respectively. It was shown that all the preserved ANAMMOX sludge could convert nitrogen, but the conversion ratios of the substrate were not a typical stoichiometry of ANAMMOX reactions. Through the formulas of different metabolic pathways, the methods of nitrogen removal were established. The preserved ANAMMOX sludge all had different levels of nitrification through materials balance. Freezing (-20°C) led to a loss of ANAMMOX activity. The ANAMMOX activity of the sludge preserved at 5°C was higher than preserved at 30°C. But the highest ANAMMOX activity resulted in being kept in a natural environment, and it had a positive linear correlation with the relative amount of substrate. The sludge activity remained at 80% when the relative amount of substrate was above seven. So short-term anoxic (£ 45d) preserved in a dark natural environment with ambient temperature between 0 to 15°C is a more economical and effective way.