Research methods: By analyzing the influential factors of reliability allocation, the method of fuzzy synthesis evaluation based on fuzzy mathematical theory was presented to carry through optimum allocation of catenary system in this paper. Namely, appointed reliability index is distributed rationally to subsystem of catenary system by establishing factor collection of reliability level and the weight of factor and further synthesis decision-making based on attachment degree of every factor. Both reliability of whole system and economic benefit are ensured, its arithmetic was programmed simultaneously.