The three high-performance indicators (low retrace tolerance, long life and low vibration) of N–N type planetary gear apparatus with small tooth number difference (abbrev "N–N–PGA") are hardly achieved simultaneously until recently. At present, the root cause analysis (RCA) and TRIZ are considered to be comprehensive and systematic new theories for technological innovation, which provides a new way to figure out the conundrum existed in the N–N–PGA. In the present study, the "root cause" of the problem is proposed with the RCA approach and two contradictions existed in the N–N–PGA have been revealed: Harmful side effect and stability of composition; harmful side effect and durability of a moving object. Besides, two reasonable principles ("Dynamicity" and "Composite materials") for the N–N–PGA design recommended by the TRIZ method are used to eliminate these contradictions. In addition, a prototype of the obtained new type N–N–PGA design is developed for experimental testing. The obtained result demonstrates the capability of the above method for obtaining low retrace tolerance, long life, and low vibration.