Incorporate parasites into trophic networks can provide new insights on structural and functional roles of parasitism in biological communities. Using recent food web data with parasites, we applied the newly developed signed digraph approach to quantify the interaction pattern for each trophic species in the food web basing on network topology. These measurements thus formed a community matrix describing the interaction strength between all species pairs in the food web. Based on this matrix, the interaction structure among the major functional groups, specifically the basal-, the middle-, the top-species and the parasites, were summarized. By modeling the interaction structure using different combinations of subwebs, i.e. predator-prey, parasite-host, predator-parasite and parasite-parasite, we found interaction pattern among functional groups were different when predator-parasite trophic links were included. To consider larval parasites as food sources for non-parasitic species not only created parasitic-bond loops of energy flow but also altered the signs and intensities of interaction structure among major functional groups in food webs. Such substantial structural alternation by parasites presents a unique feature which is typically not observed in the predation-only food web. Moreover, the cyclic pathway created by parasites may have food web dynamic and stability.