The invention discloses an overwater dredging construction method based on automatic fixed-point operation, and relates to the technical field of dredging. Comprising a mounting frame, a three-way flow dividing table, a
reamer desilting head, a filter screen, a conveying belt, an adjusting
assembly and a flow dividing mechanism, and the method comprises the following steps that firstly, the mounting frame is fixedly connected with an operation ship, and the operation ship is started to drive the mounting frame to move to the position above a
water area to be desilted; 2, according to the desilting requirement, an adjusting
assembly is started to drive a three-way flow dividing table to drive a
reamer desilting head to deflect around a hinge shaft, and the
reamer desilting head is driven to be inserted into the
underwater preset operation depth to conduct desilting operation; 3, a flow dividing mechanism is started to pull
sludge and garbage cleaned out by a reamer desilting head to penetrate through the interior of a three-way flow dividing table, and
classification treatment is conducted; and 4, the garbage which penetrates through the interior of the three-way flow dividing table and is classified by the flow dividing mechanism falls into the top of the conveying belt.