Differential Evolution (DE) algorithm is a modern heuristic algorithm has ability to solve complex, non convex and non differential problems. In this paper DE is used to solve a complex power system problem, Combined Economic Emission Dispatch (CEED). CEED has two objectives, one is to minimize generation cost and another one is minimize emission level. Price penalty factor is used to convert these two objectives problem into single objective problem and subjected to equality and inequality constraints. Proposed DE result is compared with other heuristic algorithm in the literatures, to prove its capability to solve CEED problem. In addition to this one new constraint, reactive power limit is added to the problem for the practical application. For generation cost, quadratic cost equation with valve point effect is used and for emission calculation 5 coefficients quadratic emission function is considered. Standard IEEE 30 bus, power system having 6 thermal power plants, is considered to validate the simulation.