Abstract: A microcellular thermoplastic polyurethane foamed sheet with a high foaming ratio includes components of: TPU with 70˜100 parts by weight, and polydimethylsiloxane with 0˜30 parts by weight. The present disclosure has the following advantages: because the supercritical fluid has a relatively high solubility in the polydimethylsiloxane while the polydimethylsiloxane has a relatively low interfacial tension, mixing a small amount of polydimethylsiloxane into the TPU significantly facilitates the diffusion speed of the supercritical fluid in the TPU and shortens the diffusion equilibrium time of the supercritical fluid in the TPU. In addition, a method of manufacturing a microcellular thermoplastic polyurethane foamed sheet with a high foaming ratio is further provided.