Anaerobic ammonium oxidation (Anammox) is considered to be an efficient, cost-effective and environment friendly ammonium removal process. However, the extremely slow growth rates of anammox bacteria, long doubling time and harsh requirements for environmental factors, resulted in a great hindrance in the widespread application of the anammox process. In recent years, researchers have paid more attention to promoting the start-up of anammox reactor by adding biological carriers. In this study, Granular activated carbon (GAC) and PVA-gel beads as these two types biological carriers were used in anammox reactors. There are three main research aspects as follows: (1) the effects of these two types of biological carriers on the nitrogen removal performance and start-up of anammox were compared; (2) comparison on the effects of adding two types of biological carriers on microbial immobilization and microbial activity in anammox system; (3) comparison of microbial population succession in anammox systems with two types of biological carriers added. Therefore, this study can provide a theoretical basis for the selection of anammox biological carriers.