In this paper, we study L-2 gain property for a class of switched systems which are composed of both continuous-time LTI subsystems and discrete-time LTI subsystems. Under the assumption that all subsystems are Hurwitz/Schur stable and have the L-2 gain less than gamma, we discuss the L-2 gain that the switched system could achieve. First, we consider the case where a common Lyapunov function exists for all subsystems in L-2 sense, and show that the switched system has the L-2 gain less than the same level gamma under arbitrary switching. As an example in this case, we analyse switched symmetric systems and establish the common Lyapunov function explicitly. Next, we use a piecewise Lyapunov function approach to study the case where no common Lyapunov function exists in L-2 sense, and show that the switched system achieves an ultimate ( or weighted) L-2 gain under an average dwell time scheme.