The Belt and Road Initiative (BRI) is a Chinese strategy, proposed to strengthen the connectivity and cooperation among BRI countries. Under this circumstance, many transportation projects are planned to be carried out, which means the transportation accessibility evaluation is of significance in providing valuable suggestions for transportation construction. This research established a global transportation accessibility index (GTAI) model in the BRI region using raster data. Based on its gridded outputs, we conducted classification evaluation, autocorrelation analysis, and a geographical weighted regression model to explore the spatial characteristics of the GTAI distribution and its correlation with population density. The results show that: (1) most countries in Europe and the Middle East, western Russia, and eastern China enjoy high accessibility, while central regions (e.g., Central Asia and western China) have poor access to destinations; (2) the GTAI values are distributed as a spindle, where about 60% areas belong to the middle transportation accessibility region, mapped as a non-significant type; and (3) there is a positive relationship between transportation accessibility and population distribution, but their connection tends to be weaker as socioeconomic development increases. Finally, several policy implementations are provided: (1) give a priority to road or railway construction between China and Central Asian countries; (2) establish an innovative transportation system and introduce advanced technologies to enhance the exchange and cooperation among the BRI countries; (3) improve public transport management in well-developed regions, and introduce talents and strengthen transportation infrastructure construction in developing regions.