In order to meet the related engineering quantity computing rules of shotcrete and lining concrete in TZJ 20032017 Budget Quota of Railway Project (Chapter 3: Tunnel Engineering), the unified calculation rules of backfill quantity and cost of tunnel overbreak is studied. Based on the general referenced sketch of doubletrack tunnel of 350 km/h passengerdedicated line and related design codes and construction technology regulations, the simple and convenient calculation rules of quantities of allowable overbreak and reserved deformation and quantity and cost of tunnel backfill are proposed; and the quantity and cost of tunnel backfill under different surrounding rock grades calculated by new and existing budget quota are compared. The results show that by adopting the new budget quota, the quantity of tunnel backfill decreases under surrounding rock grades of Ⅱand Ⅲ, while increases under surrounding rock grades of Ⅳ and Ⅴ, and the quota cost of tunnel backfill increases by RMB 700 per meter to RMB 1 100 per meter.