There are at least eight kinds of different potassium channels on cardiac cell membrane. This paper presents a nonlinear property membrane outward current going rectifying potassium channel and the inhibitory effects of oxygen free radical on this channel. The current-voltage relation of this nonlinear-membrane can be defined by an equation I = 8a3/(0.01v2 + 4a2)2 and the maximum conductance of this channel is -75.3 pS.