This paper presented a joint re-source allocation (RA) and admission control (AC) mechanism in software defined mobile networks (SDMNs). In this mechanism, the joint RA and AC problem can be formulated as an optimization problem with the aim of maximizing the number of admitted users while simultaneously minimizing the num-ber of allocated channels. Since the primal problem is modeled to be a mixed integer nonlinear problem (MINLP), we attain the suboptimal solutions to the primal MINLP by convex relaxation. Additionally, with the glob-al information collected by the SDMNs con-troller, a centralized joint RA and AC (CJRA) algorithm is proposed by the Lagrange dual decomposition technique to obtain the global optimum. Meanwhile, we propose an Open-Flow rules placement strategy to realize CJRA in an efficient way. Moreover, a distributed al-gorithm is also developed to find the local op-timum, showing a performance benchmark for the centralized one. Finally, simulation results show that the proposed centralized algorithm admits more users compared with the distrib-uted.