The invention discloses a flow measuring device capable of seamlessly switching ranges, and belongs to highly-integrated flow measurement devices. The flow measuring device structurally comprises a wing-shaped flow guiding plate bent pipe and a multi-chamber integral multifunctional measuring transmission device. A single chip microcomputer automatically selects whether a pressure mechanical amplification device is used or not, changeable range functions are finished, the single chip microcomputer automatically selects suitable pressure difference chamber measuring results, and corresponding system flow is outputted through digital quantity by the aid of measured system temperature and pressure. The device automatically selects the maximal position of pressure difference of the bent pipe to measure under different flow conditions, measuring accuracy is ensured, and the ranges of the whole process are automatically changed. The device can be efficiently applied to high-temperature and high-pressure systems, systems with large flow difference under different working conditions, systems with high flow resistance requirements and low-flow systems. The device is reasonable in system design, low in cost and convenient to operate, and signals are accurate and easily read.