Abstract: With the problems of high cost and low biogas yield in traditional acidification recovery method of anaerobic digestion (AD), the paper selected steel slag added in the biogas production recovery method, which was the by-product of steel making, and the effect of steel slag on the recovery after acidification was compared with that of alkali. The results showed that the acidification system could be restored by adding steel slag and alkali on the first day, and the cumulative biogas production rate on the 40th day was 285.33 mL/g with the steel slag adding, which was increased by 25.8% compared with the traditional method of adding alkali. At the same time, the pH values, total volatile fatty acid (TVFA), alkalinity (TA), and volatile fatty acids (VFAs) of the steel slag and alkali groups after recovering biogas production were monitored and analyzed. The TVFA was slowly decreased till exhausted and the TA was basically around 12.45 g/L in steel slag group; on the contrary, the TVFA increased in first 2 days and then decreased and the TA slowed down till 8.72 g/L in alkali group. And the t test was used to analyze the data variation of biogas yield, TA, TVFA and pH value in alkali and steel slag groups (each group had 21 samples), the significant level of the biogas yield (0.005) was less than 0.05, while the significant levels of TA, TVFA and pH value were more than 0.05. Therefore, the biogas yield in the 2 groups was significantly different, but the difference of TA, TVFA and pH value was not significant. Meanwhile, the trend of acetic acid, propionic acid, butyric acid and lactic acid was observed. The results demonstrated that the recovery rate of each kind of acid in steel slag group was 3-4 d faster than that in alkali group, and the order of recovery rate was successively butyric acid, lactic acid, acetic acid and propionic acid; the significant levels of acetic acid, lactic acid, propionic acid and butyric acid were 0.064, 0.068, 0.076 and 0.098, respectively, all greater than 0.05, which indicated that the differences among the 4 kinds of acids were not significant in the recovery stage. The ratio of TVFA to TA and the ratio of propionic acid to acetic acid were studied, and the results indicated the 2 ratios in 2 groups were both at the best level after recovery for 15 d, and on the 8th day the 2 ratios in steel slag group dropped to 0.38 and 0.081, respectively, and then decreased to below 0.05; there was the same trend in alkali group. The P values of the ratio of VFA to TA and the ratio of propionic acid to acetic acid between alkali treatment and steel slag treatment were 0.15 and 0.26, respectively, which were all more than 0.05, indicating that the changes of data in these 2 ratios were not significant. This showed that the 2 systems could be recovered quickly in the recovery stage. At the last, the content of heavy metals in the digestive juice after recovery was analyzed, and the results indicated that the 2 kinds of biogas producing methods fully satisfied the requirements of the technical specification of NY/T 2065-2011 biogas fertilizer application. The paper provides a way to recover biogas from the traditional regen acidification liquid, which solves the problems of the easy acidification of the actual engineering and the high cost of the recovery of biogas production.