The invention provides a reservoir underwater walking sand suction and discharge device. The device comprises a working ship, a water pump, an air pump, a windlass and a positioning system arranged on the working ship, and a porous sand suction disc arranged on a silting bed surface of the bottom of a reservoir. An annular air cavity is formed in the porous sand suction disc; a sand punching hole and a sand suction hole are formed in the porous sand suction disc; the water pump is communicated with the sand punching hole through a water charging pipe; the sand suction hole is connected into a dam sand discharge hole through a sand conveying pipe; the air pump is communicated with the annular air cavity through an inflation pipe; and the windlass is connected with the porous sand suction disc through a traction steel rope. The device is arranged in a reservoir area; high-pressure water is injected in the sand punching hole of the porous sand suction disc through the water pump for dispersing and disturbing silted sediments of the reservoir; a high-concentration water and sand mixture is sucked through the sand suction hole of the porous sand suction disc and the sand conveying pipe for realizing efficient dam passing of the silted sediments of the reservoir; the dispersion, the disturbance and the suction of the silted sediments at the bottom of the reservoir can be synchronously realized; high-concentration muddy water is easy to form; the water consumption is low; and the sand sucking and desilting efficiency is high.