Interference is a key factor that impacts the performance of wireless networks, especially when each node is equipped with multiple interfaces. Based on the classification criterion presented in this paper, we classify current interface assignment strategies into three types: static, dynamic and hybrid. We mainly address the problems of characterizing and evaluating interference effects of static strategy and two hybrid strategies in multi-interface wireless mesh networks. We prove that, if all links are bi-directional, both hybrid strategies described have identical interference characteristics. We derive formula for computing interference node set and channel interference possibility respectively. We also present an extensive evaluation via NS2 simulations. Compared to static strategy, the hybrid strategy yields more throughputs, higher traffic fairness and faster adaptation to traffic changes.