In view of the current situation that landscape waterfronts are small, dispersed, increasing, and it is difficult for big mowers to cut aquatic grass, a small type submarine mower-SGW1.2 type submarine mower, is developed for small waterfront. Based on the definition of the swath, the cut depth, the machine’s outline size, productivity and other technical parameters, and combined with the knowledge of hydrodynamics and theoretical naval architecture and so on, the reciprocating cutters, propeller and auxiliary structures are selected and designed, and then the design of the submarine mower is accomplished. The experiments showed that SGW1.2 type submarine mower’s cutting depth is adjustable among the required range, and all the parameters including the turning radius, the productivity, the speed and the fuel consumption meet the demands as anticipated. The average omission rate and average cutting leakage rate are small. The experiments proved that the submarine mower has a good ability for continuous cutting and harvesting, and is appropriate to cut aquatic grass in small-scale waterfronts.