This paper studies the channel asymmetric characteristic between a downlink and an uplink channel in orthogonal frequency division multiple access (OFDMA)/time division duplexing (TDD) systems. To investigate the downlink and uplink channel asymmetry, we derive a propagation loss model and a shadowing model taking into consideration geometrical information and inter-cell interference. Then, the channel asymmetric cases are introduced based on the proposed channel models. Numerical results show that the causes of the uplink and downlink channel asymmetry are mainly due to the coverage of neighbor cells and the usage ratio of uplink and downlink traffic. As coverage of neighbor cells increases, an uplink signal to interference and noise ratio (SINR) becomes lower than that of a downlink SINR. In addition, as uplink traffic of mobile stations (MSs) increases, an uplink SINR decreases. increases.