Based on corpus, this paper analyzes the diplomatic discourses of Ukraine and Russia to explore how proximization strategies are employed to legitimize their discourses and uncover the underlying reasons. The study reveals that spatially, Ukraine’s diplomatic discourse exhibits a stronger spatial-proximization-dominated feature than Russia’s, with both constructing distinct IDCs and ODCs. Temporally, Russia’s diplomatic discourse emphasizes “past-present” temporal proximization, while Ukraine’s discourse highlights the “future-present” span. Axiologically, Ukraine rationalizes its discourse through values of “regularity” and “westernization”, whereas Russia underscores justice rooted in “historical”values. Differences in interest selection within communicative games and variations in social cognitive perceptions of national identity may account for the distinct proximization features in the diplomatic discourses of the two sides. The findings may reveal the ideological drivers behind discourse legitimization and shed light on the interactions between discourse, power and social reality.