The invention provides a method and system for combusting biomass-containing waste through a coal-fired boiler. The system comprises a boiler hearth for combusting biomass, a bin for storing the biomass, a decomposition and combustion platform arranged at the boiler hearth, a cooling system and a feeding system connected with the bin and used for conveying the biomass to the decomposition and combustion platform. The method and the system are characterized in that the decomposition and combustion platform is composed of a plurality of hollow pipelines arranged side by side, an inlet header andan outlet header, the decomposition and combustion platform is adjacent to a boiler wall and inclines downwards by a certain angle in the horizontal direction, a feed inlet is formed above the junction, and the biomass enters the hollow pipelines via the feed inlet and is decomposed and combusted step by step by means of high-temperature radiant heat in the boiler hearth. According to the methodand system for combusting the biomass-containing waste through the coal-fired boiler, the biomass can be treated by the coal-fired boiler, so that waste recycling is achieved, and meanwhile, as dioxinis fully decomposed through high-temperature air flow of the coal-fired boiler, harmless treatment of the waste is achieved.