The invention discloses an ammonia method-tower type system and process for collecting and absorbing carbon dioxide at normal pressure. The system comprises a dilute ammonia water supply device and the like; a carbon dioxide absorbing tower comprises a tank body and the like, wherein the top of the tank body is provided with an exhaust pipe, the dilute ammonia water supply device is connected with a first spraying device through a pipeline, a draught fan is connected with a first heat exchanger through a pipeline, the first heat exchanger extends into the lower part of the tank body through apipeline; the bottom of the tank body, a second pump, a second heat exchanger, a crystallization tank, a centrifugal machine and a mother liquor tank are sequentially connected through a pipeline; the mother liquor tank, a third pump and a second spraying device are sequentially connected through a pipeline; a first pipeline is connected between inlets of the second pump and the third pump; a high-concentration ammonia water storage tank is connected with the first pump through a pipeline, the first pump is connected with the second spraying device through a pipeline, a cooling water inlet pipe of a cooling device is connected with a cooling water inlet pipe of the first heat exchanger together; and regulating valves are arranged on the cooling water inlet pipes. The invention has the advantages of high carbon-reducing efficiency, simple process, simplified system structure and low investment and operation cost.