Water sampler with adjustable sampling depth range

The invention discloses a water sampler with the adjustable sampling depth range. The sampler comprises a sampling pipe and a positioning device, wherein a one-way water stop device is arranged at thelower end of the sampling pipe; the positioning device comprises a push rod and a positioning piton fixed to the bottom part of the push rod; the positioning piston is arranged in the sampling pipe;the upper part of the push rod stretches out of the sampling pipe; the positioning piston comprises a circular ring-shaped piston piece, a permeable ball cover and a small ball; the ball cover is fixed above the piston piece; the small ball is located in the ball cover and can move up and down; the diameter of the small ball is larger than the inner diameter of the piston piece; the push rod is fixed to the top part of the ball cover; the periphery of the piston piece is sealed with a pipe wall of the sampling pipe; through pushing the push rod, the positioning piston can move up and down along the pipe wall, so that t