To further reveal the structural characteristics of moss mitochondrial genomes from the still unexplored orders, we sequenced and assembled the mitogenome from the granite moss Andreaea wangiana (Andreaeaceae, Andreaeales). The newly generated genome consisted of 117,857 base pairs with an average GC content of 42%. The gene contents and gene order were found to be identical to those previously published from mosses, reconfirming the hypothesis of structural conservatism in this lineage. Comparison of the newly generated mitogenome with those published suggested an evolutionary trend towards size reduction of mitogenomes across the tree of mosses. The pattern was largely caused by hierarchical loss of introns and/or shortening of intergenic spacers. We found evidence to support a positive correlation between GC content and genome size in bryophytes. Furthermore, we identified 233 putative RNA editing sites for all protein-coding genes and 60 simple sequence repeats in this mitogenome. By reporting the complete mitogenome from an important early diverging lineage of mosses, this study provided valuable data for further studies to explore the mechanisms maintaining the stability of genome structure during nearly 400 Ma of independent adaptation to changing terrestrial environments. The study further identified a few highly variable regions that could be used as DNA markers to clarify the genetic diversity of granite moss populations.