The invention belongs to the technical field of internal combustion engines and relates to a single-side crankshaft connecting rod hydraulic engine which is featured with novel structure and used for energy conversion and output; wherein an energy conversion structure is a crankshaft connecting rod structure consisting of a piston, a plunger, a crankshaft and a connecting rod which are matched with one another; the structure of the piston is the same as that of the traditional internal combustion engine, both ends of the connecting rod are in same thickness; the lower part of the plunger matched with a sliding sleeve is cylindrical; the shape of a middle structure is determined according to strength, a connecting rod journal in the lateral direction is arranged on the middle structure and in clearance fit with a second sliding bearing; the connecting rod and the second sliding bearing can rotate flexibly; the structure of the crankshaft is a half of the crankshaft of the traditional single-cylinder piston engine, the principal shaft journal is relatively long, by the supporting of a first bearing and a second bearing, the connecting rod journal of the crankshaft is in clearance fit with a first sliding bearing, the connecting rod and the first sliding bearing rotate flexibly, a cavity of a machine body is a hollow shell, and a flange at the lower end is provided with a plurality of circular holes; the engine has advantages of short energy conversion and transmission route, high efficiency, compact structure, easy starting and stable operation.