How to enhance the efficiency of high order harmonic generation is an important topic in high field physics. Many ways including two color laser field, phase matched in a gas filled hollow fiber and adding a magnetic field, etc. are adopted. In the investigation of two color field high order harmonic generation, it is found that the atomic energy level structure greatly affects the high order harmonic generation. For a certain level structure, a specially chosen high frequency additional driving field can greatly enhance the efficiency of high order harmonic generation.