Water flow power generation apparatus, includes an upper bracket and a lower bracket. The transmission and the generator are located above the upper bracket, there are at least two reverse direction rotating water wheels fixed between the upper bracket and the lower bracket. Every vane of one wheel extends into the space between two adjacent wanes of the other wheel, and the same end of each water wheel is fixed with some synchromesh gears, respectively. A sharp-angled shape guide object is fixed at the water inlet end of the water wheels between the upper bracket and the lower bracket. The resulting structure can not only improve the utilization ratio of water power, but also improve the generating efficiency; moreover, the whole generating apparatus is of simple structure, low cost for design and manufacture and easy installation, and applicable to various water flows.