The blow-by which occurs in a coaxial plasma gun is the result of reinforcing feedback caused by the gradient of magnetic field and the component of axial current due to the canting of current sheath. The blow-by has become a serious negative effect which limits the effective use of the coaxial plasma gun, so it is necessary to study by experiment the parameters that influence the degree of blow-by. This will not only contribute to the study of the theory and mode about blow-by but also give advices to the weakening or eliminating blow-by by choosing suitable parameters in engineering field. The degree of blow-by can be observed directly by photomultiplier, and the influence of voltage of capacitance, capacitance, and the pressure of gas on blow-by have also been studied. It is shown that the blow-by would become more serious with the increase of capacitance or the voltage of capacitance while it becomes weaker with the increase of gas pressure. These phenomena can be explained based on the snowplow model. We consider that the increase of capacitance or the voltage of capacitance can make the current sheath canting more serious, however it would reduce the degree of current sheath canting with the increase of gas pressure. So the blow-by can be controlled by the parameters which influence current sheath canting.