The invention relates to a bottom-sitting all-weather bed load sediment real-time monitor and a measuring method thereof. The monitor comprises an outer barrel of a sand collecting barrel and an inner barrel, arranged inside the outer barrel, of the sand collecting barrel, wherein a signal output end and an underwater pressure gauge which contains a smart device and connected with an outer control device are arranged at the bottom of the outer barrel; the top end of the underwater pressure gauge is fixedly connected with the bottom end of the inner barrel; a sand discharge pump is arranged in the inner barrel; a sand flushing pump is arranged outside the sand collecting barrel; controlled ends of the sand discharge pump and the sand flushing pump are connected with the outer control device; and a barrel cover with an annular cross section is arranged at the top end of the outer barrel, a barrel cap is arranged above the barrel cover, and a sand filling port is formed between the barrel cap and the barrel cover. According to the monitor and the measuring method thereof, the design is reasonable, the underwater pressure gauge and the outer control device are matched for use, so that continuity and automation for bed load measurement are achieved, change of the bed load sediment in the river bottom can be measured accurately without influence of environmental factors such as water depth, wave, external sediment and the like, continuous sampling of the bed load sediment in rivers is achieved, and the monitor and the method are suitable for measurement work of bed load sediment discharge of rivers with fine particle sediment.