This letter proposes a Per-Unit modeling standard (PUMS) for simplified calculations in grid-forming converter (GFMC) systems, which can improve and simplify the modeling process. The proposed PUMS can solve the bottlenecks and difficulties of calculation, caused by the upper limits of calculation in MATLAB, while developing large-scale grid-integration of GFMC. Besides, the proposed PUMS is well matched with actual value modeling. And the switching modeling is compared by the average model with coincidence to verify effectiveness. Finally, modeling and analysis are validated by simulations and experiments.