Abstract: Light oil filling system inside oil depot includes tanker truc's filling and oil barrel's filling, with two filling methods: pumping and gravity flow. Aiming at the relationship between necessary cavitation allowance (Δh) of oil pump and cavitation allowance (Δh_a) of unit involved in pumping filling, release protection of products in gravity flow filling and further analysis into filling practice, pointed out that when setting up each oil pump individually, new reflex pipeline and selecting flow meters, solving method at normal flowrate in product flowing across flow meter in the center and at slightly downstream area of the flow meter should be taken into consideration.