A 20-in. photomultiplier tube based on dynode and microchannel plates (Dynode-MCP-PMT) with high collection efficiency (CE) and good time performance is proposed in this article. To obtain a tailless time distribution, a pair of uncoated MCPs are employed. For a high CE, a dynode with two large openings is placed in front of the MCPs. The dynode is designed as a spherical shape to prevent secondaries from escaping the multiplication system and assist them moving to the MCPs for further multiplication. A 3-D model is developed by CST Studio Suite to validate its feasibility. Finite integral technique and Monte Carlo method are combined to simulate the photoelectron collection and multiplication processes. Results predict that for the shielded Dynode-MCP-PMT, CE is expected to be 100%. Tailless transit time distributions are observed. Transit time spread (TTS) of the photoelectrons from the cathode top point to the dynode achieves 3.7 ns. If this PMT is exposed to the geomagnetic field, it should be operated in the north and south direction, in which CE and TTS are expected to be 100% and 3.8 ns, respectively.