The present study calculates correlation energies of the different length poly(pphenylenevinylene) (PPV) units using the formula recently developed for π conjugated polymers, and analyzes the correlation energies from the phenylene unit and the vinylene unit in single and three PPV unit cells as well as the effect of the correlation energies on the band energy gap of the PPV. The present method avoids the complicated numerical computations about the correlation effects for the π electronic conjugated molecule systems with large unit cells.