In tokamak plasmas, the discharge will turn into "runaway" discharge if the density decays to a critical one. The discharge will enter into "slide-away" discharge if the density reaches a lower level. The slide-away discharge is characterized by high confinement of superthermal electrons which constitute a large part of plasma current. In HT-7 Tokamak, the slide-away discharge is achieved by reducing the plasma density. The relationship between plasma current and critical density of slide-away discharge is investigated. It is also find that the increase of density in slide-away discharge can make the confinement of superthermal electrons poor and lots of superthermal electrons lost from the vacuum chamber.