Abstract: This paper studies the method of source stirring, especially using multiple sources to improve the field uniformity in reverberation chambers (RCs). Firstly, the factors that may affect the field distribution in RCs are summarized, according to the Maxwell’s equations in ideal rectangular resonators. Then the focus is on the effects of multiple sources on the electromagnetic field distributions in RCs, including the maximum and the standard deviation of electric field strength and the isotropy as well. The results show that multiple sources can improve the field uniformity effectively and are useful in constructing a homogenous electromagnetic field environment for high-power microwave effect test on subsystems.