The invention discloses a fine-grained Web3D online visualization method for a large-scale building scene, and the method comprises the steps: firstly, carrying out lightweight preprocessing in a model-level fine-grained mode and a file-level fine-grained mode in a BIM model lightweight preprocessing stage; secondly, in the network end pre-rendering and transmission scheduling processing flow, loading preprocessing, optimal initial viewpoint selection, visual increment list calculation, interestingness calculation, file packaging and the like are included; and finally, in a Web end multi-thread asynchronous loading and rendering process, firstly performing incremental downloading on visual component data in a scene through multiple threads, making online efficient analysis on a file package by a WebAssembly technology, then carrying out instantiation rendering by using reuse information of the component, and carrying out component loading and removal management by a cache scheduling mechanism based on interestingness. Through the process processing, a set of progressive lightweight online visualization solution for a large-scale BIM scene is completely realized.