The performance and syntrophic metabolism of the Anaerobic Membrane Bio-reactor (AnMBR) treating high-lipid kitchen waste slurry under different sludge cycle frequencies were investigated in this study. When the sludge cycle frequencies were 3.6 cycles/h, 9.0 cycles/h and 14.4 cycles/h, the obtained Organic Loading Rates (OLRs) were 10.3 kg-COD/m³d, 12.4 kg-COD/m³d and 18.1 kg-COD/m³d, while the corresponding biogas productions were 190 L/d, 310 L/d and 520 L/d. Moreover, with an increase of sludge cycle frequency, the Chemical Oxygen Demand (COD) removal efficiency improved from 86.2% to 90.4% and 96.3%. Additionally, the higher sludge cycle frequency did not break up the sludge flocs and further affect the syntrophic degradation of the toxic Long-Chain Fatty Acids (LCFAs). Conversely, the higher sludge cycle frequency enhanced LCFA degradation and decreased LCFA accumulation. Meanwhile, under higher sludge cycle frequencies, the abundance of syntrophic Methanobacterium, Syntrophomonas and Clostridium increased and favored the syntrophic metabolism of LCFAs.