The moving-grate gasifier has some significant advantages over other types of gasifiers. This is because the residue time of the biomass waste in a moving-grate gasifier can be controlled in a suitable range for optimizing thermochemical conversion efficiency. In addition, the moving-grate gasifier is more suitable for having biomass waste fed into it. This study investigated the gasification behaviours of biomass waste in the moving-grate gasifier with the addition of all air being done in the oxidizing stage. In the experimental samples, the average cold gas efficiency in the moving-grate gasifier was 64.79 %, and the high temperature region in the moving-grate gasifier was converted to the pyrolysis. The lower heating value (LHV) of flue gas in the large-scale moving-grate gasifier was 5570 kJ/m(3) and the cold gas efficiency was 67.50 %. From this observation, it can be concluded that the gasification performance of the large-scale moving-grate gasifier was better than that of the small-scale. (C) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.