The concept of work lot length is brought into TZJ 2003—2017 Budget Quota of Railway Tunnel Works so as to unify the concepts of tunnel length, converted tunnel length and total tunnel length. Nevertheless, the understanding differences of work lot length under different construction organization conditions would lead to different using deviations. The calculation principle of work lot length of railway tunnel is analyzed by the maximum dead end distance method, converted tunnel length method and definite integral method; the application problems of calculation rules of work lot length of railway tunnel to the length of work lot and quantities of ventilation and pipeline are discussed; a simple and practical calculation method and principle are proposed; theoretical basis of the work lot length of tunnel crossing section calculated by twice is demonstrated; and the principle of configuration according to actual conditions and rational share for calculation of ventilation and pipeline and the specific analysis and calculation method according to construction organization are put forward.