The invention provides a fin type heat exchanger which comprises a plurality of fin plates, coiled pipes passing through the fin plates, and diversion trenches connected with the lowest points of the lower ends of the fin plates; the horizontal heights of the lower ends of the fin plates are increased gradually; the edges of the lower ends of the fin plates are arranged in an inclining manner; the coiled pipes are spiral or waved bend pipes. The fin type heat exchanger can prevent condensate water from frosting into ice to take bad effects on the heat exchanger, increases the turbulence degree of fluid in the coiled pipe, enhances the heat or cold transfer, and improves the heat transfer effect of the heat exchanger.