The electron impact ionization cross sections for different energy assignment on two final-state electrons (energy differential cross sections) of heliumlike ions have been calculated by using a disrored-wave Born exchange approximation. We found that the dependence of the differential cross sections on the scaled energy of secondary electrons can be well fitted with a two-parameter Gaussian function. The dependence cf two parameters on the incident electron energy and target charges have been given. The differences between the results from CBE (Coulomb-Born exchange approximation) and DBE calculations have been discussed. They show that it is necessary to use DBE calculation for low target charges and low incident en-