A novel in-situ nano hybrid technique combined with industrialized wet phase inversion coating-forming process was developed for the modification of polyurethane (PU) leather coating with nano-$SiO_2$. During the wet phase inversion process, nano-$SiO_2$ particles were in-situ generated synchronously as polyurethane resin coagulated. Scanning electron microscope analysis indicated that when the $SiO_2$ concentration was limited within 1.5 wt%, the size scale of in-situ generated nano-$SiO_2$ ranged from 70 to 150 nm, which were well-separated and dispersed uniformly throughout the PU coating. After nano hybridization, extra mesopores were detected in the PU coating by nitrogen adsorption/desorption experiment. These mesopores were correlated with enhanced water vapor and gas (hydrogen, nitrogen, and oxygen) permeability, which could improve the breathability or wear comfort of PU leather. In spite of extra mesopores, the hybrid PU coating maintained comparable hydrostatic pressure to control. Nevertheless, when the $SiO_2$ concentration was increased up to more than 1.5 wt%, micro-$SiO_2$ particles and agglomerates dominated throughout the PU coating, which obstructed mass transportation and lowered the breathability of the coating. Without disturbing established wet phase inversion coating-forming process in PU leather industry, the novel in-situ nano hybrid technique developed in this study may be of great potential for producing PU leather with improved breathability on an industrial scale.