The continental slope is a relatively steep transition zone between a low-gradient marine shelf and the deep seafloor. It has unique geographic ecological enviroment and actively exchange of energy and matter fluxes. Based on the survey data of fishery resources and marine ecological environment in the continental slope of northern South China Sea during 2015-2016, we developed a mass-balance model, which consists of 22 functional groups, using Ecopath with Ecosim software. Based on the model, we analyzed the trophic structure, energy flow and system attribute. The fractional trophic levels of these ecological groups ranged from 1 to 4.47, with the highest TLs reached by dolphins in the food-web system. The Keystone Index (KSi) analysis indicated that the mesozooplankton and Sthenoteuthis oualaniensis are considered as key species in the system. The energy flow of this ecosystem was mainly dominated by detritus food chain, which accounts for 52% of the energy source. Using network analysis, the system network was mapped into a linear food chain and 6 integrate trophic levels were found with a mean transfer efficiency of 21.94%, of which 21.26% from primary producer and 22.39% from detritus within the ecosystem．The results suggest that the continental slope of northern South China Sea ecosystem has a high ecological conversion efficiency.