LTE TDD has received increasing attention in the next-generation wireless networks, due to its ability of dynamic allocations for uplink and downlink spectrums. In this paper, we evaluate the system performance with a simple flexible TDD switching scheme by system level simulation. The scheme considers switching among three different TDD configuration structures, based on the empty/non-empty buffer conditions of uplink and downlink data traffic, in order to allocate radio resources more efficiently. The system performance is evaluated with a system level simulator, under the practical parameter settings in 3GPP LTE system. The numerical results show that there are certain gains in terms of throughput for both uplink and downlink by the proposed flexible TDD switching scheme, compare with fixed TDD.