The cascade four-level system has six possible optical transition channels and provides many real subtypes for theoretical and experimental studies about quantum coherence effects. Using Boolean algebra method, according to possible existing transition channels, combining electric dipole selection rule, all channel subtypes of cascade four-level scheme are studied, the realistic channel subtypes of 17 three transition channels and 2 four transition channels are got. Furthermore, 168 real intensity subtypes appear when one distinguishes each of related laser field intensities only. This multiformality of realistic channel and intensity subtypes provides more subtle energy level scheme-choosing chances for quantum optics, quantum information science, precise laser spectroscopy, etc.