Owing to the climate change and energy crisis, harvesting energy from our surroundings and the construction of self-powered wireless environmental monitoring systems are promising approaches in modern times. In this paper, an ultra-compact highly efficient miniaturized windmill comprising a hybridized nanogenerator (MW-HNG) is reported based on three conversion mechanisms i.e. triboelectric nanogenerator (TENG), piezoelectric nanogenerator (PENG), and electromagnetic generator (EMG). The MW-HNG is designed as a 3D-printed fully-enclosed structure for the natural wind energy harvesting by converting into rotational motion: all harvesting units reside in a common rotation system to effectively and simultaneously produce electricity. At a wind speed of 6 m/s, the flexible-blade-based hybridization-mode (contact–lateral sliding–separation–contact) TENG and coupled PENG can generate maximal power values of 1.67 mW and 1.38 mW at optimal load resistances of 10 MΩ and 330 KΩ, respectively. In contrast, the multipole-magnet-based EMG can obtain a maximal output power of 268.6 mW at 180 Ω. The MW-HNG demonstrates a quick charging ability for capacitors and the capability to feed hundreds of LEDs. Further, a self-powered wireless sensor system is developed for real-time environmental monitoring by combining an MW-HNG, a customized power management circuit, and wireless sensor unit (a smartphone to display sensor data). Our proposed MW-HNG is suitable for self-powered wireless sensor networks (WSNs) in the subway system by generating high-power electrical output from moving-induced wind mechanical energy.