A thermophilic anaerobic up-flow anaerobic sludge bed (UASB) was rapidly established from a mesophilic reactor in 25 days by directly increasing the operation temperature from 35 to 55℃. The succession of methanogenic microbial community and response of antibiotic resistance genes (ARGs) during the startup period were revealed by 16S rRNA gene amplicon sequencing and metagenomics analysis. After the temperature was increased, thermophilic hydrotropic Methanothermobacter outgrew aceticlastic Methanosaeta and the mesophilic hydrotropic methanogens (Methanobacterium and Methanolinea), with its abundance increasing from 3.19% on day 7 to 72.33% on day 10. Meanwhile, Exilispira, an acetate-oxidizing bacterium, proliferated quickly in the fermenter community concurrently with the growth of Methanothermobacter, indicating that the syntrophic relationship between acetate-oxidizing organisms and hydrogenotrophic methanogens is the primary pathway for methane production in thermophilic UASB. As for ARGs, the abundance of the resistome of the anaerobic sludge decreased after the hike in temperature, driven by the succession of the methanogenic community, confirming the benefit of thermophilic treatment for antimicrobial resistance control. The results proved that a thermophilic UASB could be rapidly constructed by a one-step startup strategy due to the fast establishment of the syntrophic acetate oxidation pathway, and maintain better ARG control performance than its mesophilic counterpart.