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 M Omega and 330 K Omega, respectively. In contrast, the multipole-magnet-based EMG can obtain a maximal output power of 268.6mW at 180 Omega. 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.