The invention provides a method and a device for dynamically determining the polarization mode of a base station emitting antenna and the space coding mode in a multi-input and multi-output system. The base station of the multi-input and multi-output system firstly sends measurement auxiliary signals by at least one antenna polarization mode and one space coding mode to a mobile terminal under themanagement of the multi-input and multi-output system; the mobile terminal detects the quality of the signals after receiving the measurement auxiliary signals, generates the information correlativeto the signal quality and feeds the information back to the base station; the base station determines the polarization mode of the emitting antenna and the space coding mode of data used when the basestation sends subsequent signals to the mobile terminal according to the information after receiving the information correlative to the signal quality. Compared with the existing scheme of switchingspace coding modes in fixed antenna polarization mode, the invention can obviously improve the system capacity.