This paper investigates the theoretical system capacity of MU-MIMO Tomlinson-Harashima precoding (THP) with the ordering process. In this paper, the impact of the modulo loss peculiar to THP on the system capacity is taken into account, which makes us recognize the significance of its impact comparing with the Shannon-Hartley-based results. Moreover, the ordering process generally performed before THP to enhance the system capacity is also considered in our performance analysis. In detail, the impact of the modulo loss is analyzed by using the mod-A channel, where the result of the V-BLAST-like suboptimum ordering is reflected as the power normalization factor. The proposed performance analysis considers these two actual effects, which provides a fair comparison between THP with ordering and linear precoding (LP) as well as the impact of the modulo loss, which has great potential to improve user scheduling techniques that require accurate measurements of the instantaneous system capacity.