Abstract: Objectives： Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) are traveling, quasi-periodic wave-like structures of electron density in the ionosphere, typically characterized by horizontal wavelengths of hundreds of kilometers and propagation velocities ranging from tens to hundreds of meters per second. MSTIDs can induce ionospheric fluctuations on the order of several Total Electron Content Units (TECU), severely affecting the service performance of navigation positioning and short-wave communication systems. Therefore, investigating their occurrence and spatiotemporal variation characteristics is of great significance. Methods： In this study, differential Total Electron Content (dTEC) data from the Japanese GEONET network in 2018, a low solar activity year, and 2024, a high solar activity year, are used. An image-based AI detection and feature matching method is applied to analyze the variation characteristics and differences of MSTID spatiotemporal features over Japan under different solar activity levels. Results： The results show that the total numbers of MSTID events in 2018 and 2024 are 982 and 606, respectively. MSTIDs exhibit significant seasonal and local time dependence, with nighttime events being dominant overall. Spatially, the events show a relatively stable concentration over the central-eastern region of Honshu, Japan. In terms of propagation characteristics, the event directions in 2018 are more concentrated and mainly southwestward, whereas the propagation directions in 2024 become more dispersed. The mean propagation velocity increases from 88.5 m/s in 2018 to 108.4 m/s in 2024. Conclusions： Notably, the comparison between 2018 and 2024 shows that MSTID occurrence frequency exhibits opposite day-night variations, with an increase during daytime and a decrease during nighttime. This result indicates that MSTID occurrence under different solar activity backgrounds may have local-time-dependent variations.