The invention describes a system for testing antenna-in-package (AiP) modules and a method for using the same. Firstly, AiP modules respectively receive RF signals from a testing transmitting antenna. Then, at least one of the power and the phase of each of the RF signals is adjusted to generate modulated RF amplified signals as recognition tags with difference. The RF amplified signals are received from each control integrated circuit (IC) and the power of the modulated RF amplified signals is summed to generate a net mixed test signal. Finally, the test signal is received and RF properties corresponding to at least one of the power and the phase of each of the RF amplified signals as recognition tags are obtained. The method can simultaneously test a plurality of AiP modules to shorten the test time.