We describe about characteristics of creeping discharge developed in a partial narrow space with a backside electrode，under μs pulse voltage application. As a result，in the case of a filamentous straight backside electrode at 0.3MPa; flashover voltage decreased from about 16.4 kV to 15.0kV by 3% SF6 mixture in N2.V- characteristics of which flashover voltage decreased were obtained by SF6 mixture in N2. We obtained V-characteristics on the flashover voltage of SF6 content at D =0% -10% for a filamentous backside electrode (φ; filamentous backside electrode diameter，about φ=0.9mm). The behavior of V-characteristics of flashover voltage depened on a partial narrow space. In the corona extension obtained using ultra-high speed camera，the flashover along the backside electrode was observed.