A unified description to maximize the work output of reciprocating internal combustion engine is given in this paper. A dual-Miller cycle as a universal cycle for reciprocating internal combustion engine has been selected and established by a new design method. The results show that the work output has linear relationship with the intake temperature, friction coefficient, working fluid, chemical energy release by combustion and heat-transfer coefficient, while there are optimal values of the cut-off ratio, pressure ratio, geometric-compression ratio, specific heat ratio and expansion-compression ratio at which the work output attain their maxima. Thus, the work output can be differentiated with respect to the optimal values and set the resultant derivative equal to zero. In this paper, the results obtained show that the maximum work output of the dual-Miller cycle is greater than that of the classical-Otto, classical-Diesel, classical-dual, Otto-Miller, Diesel-Miller, Otto-Atkinson, Diesel-Atkinson and dual-Atkinson cycles at their optimal values of the cut-off ratio, pressure ratio, geometric-compression ratio, specific heat ratio and expansion-compression ratio, as well as at the same values of the intake temperature, friction coefficient, working fluid, chemical energy release by combustion and heat-transfer coefficient.