The experimental investigation of the current-voltage relationship of homogeneous dielectric barrier discharge （HDBD） was performed in helium and nitrogen at atmospheric pressure, respectively. The experiment results agree with the simulation results. The glow diacharge mode （GDM） and Townsend discharge mode （TDM） can coexist in one multiple current peak （MCP） discharge sequence in atmospheric He MCP discharge. Moreover, the discharge modes of atmospheric HDBD can be discriminated according to the differential conductivity of the current-voltage relationship in the ascent stage of discharge current, in which the current pulse is GDM if the differential conductivity of the current-voltage relationship is negative,and it is TDM if the differential conductivity is positive. Thus we concluded that, the atmospheric N2 HDBD is TDM.