Depth-varying denoising worm tongue and multi-blade centrifugal fan

The invention relates to a depth-varying denoising worm tongue which comprises a body (1). The body (1) is an intersecting line formed by crossing of the contour curved surface of a diffuser. The intersecting line is a symmetrical curve formed by on a volute (4). The symmetrical curve sequentially comprises a worm tongue windward section (1-2), a worm tongue intermediate section (1-3), a worm tongue secondary tail section (1-4) and a worm tongue tail section (1-5) from bottom to top. The worm tongue windward section (1-2), the worm tongue intermediate section (1-3), the worm tongue secondary tail section (1-4) and the worm tongue tail section (1-5) form the basic contour surface of the worm tongue along a radius-varying fillet structure respectively. According to the depth-varying denoising worm tongue, conventional rectilinear wire structure design is abandoned; in the worm tongue wire direction, the worm tongue depth varies, the worm tongue contour fillet radius varies in the worm tongue wire direction, a v