A heat exchanger and fins thereof are provided. The fin includes a plurality of first fin units and a plurality of second fin units which are arranged in parallel and alternately, and each first fin unit includes a first louver facing an inflow direction of fluid, and each second fin unit includes a second louver facing the inflow direction of the fluid, the first louver and the second louver are arranged in parallel, and the first louver and the second louver are staggered in the inflow direction of the fluid to form a first space between the first louver and the second louver, and at least one of first louvers or at least one of second louvers has a varied width.