The inherent long decay power delay profile (PDP) in the reverberation chamber (RC) is a major challenge for accurate channel emulation of 3GPP channel model, which is widely used in performance test of the physical layer. To tackle this challenge, we propose in this paper a novel two-step "closed-loop" approach consisting of (i) a channel measuring step and (ii) a channel model synthesis step. The channel measurement step is used to capture the wireless channel of the RC. In the channel model synthesis step, an additional IQ signal convolution process is introduced prior the IQ signal passes through the channel emulator (CE). This process filters the IQ signal by an equalizer filter derived from the measured channel impulse response (CIR) of the RC obtained in channel measurement step. From the measurement results, the proposed approach is proven that able to effectively emulate typical 3GPP 5G channel model.