A series and parallel combined dual power system operates as a series combined power system, or as a parallel combined power system; the power from an engine (100) directly drive the load (120); the system engages in the operation as the series combined power system incase of a light load; the load (120) is driven by the engine in case of a normal load; an optional rechargeable device (106) is adapted to the system; either or both of a primary and a secondary dynamo-electric units (101,103) functions as a motor on the power from the rechargeable device (106) to jointly drive the load (120) with the power from the engine (100); and functions to provide power drive in case of a light load.