In this paper, we study the uplink (UL) and downlink (DL) ergodic capacity in the bidirectional dynamic network (BDN). By dynamically allocating the numbers of UL and DL remote radio heads (RRHs), BDN facilitates simultaneous UL and DL communications to accommodate the data traffic asymmetry. Assuming that the number of antennas at each RRH (M) is large, we derive the closed-form expressions for the ergodic achievable rates in BDN systems, and the theoretical results are shown to be accurate compared with the Monte Carlo simulation results. Furthermore, we investigate the performance of the limiting UL and DL rates when M goes to infinity, and it indicates that we can scale down the UL and DL power per user proportionally to 1/M to guarantee a certain UL or DL quality of service in BDN. Numerical results indicate that there exists an optimal ratio between UL and DL RRH numbers for the maximal spectral efficiency in BDN. Thanks to our proposed RRH layout which guarantees the uniformity and symmetry in the whole network, we can find the optimal ratio between UL and DL RRH numbers more easily.