Abstract: Based on some filament current models, which are usually used nowadays, the equation of force-balance of a current filament in the vertical direction has been deduced. The effects of the two kinds of cuurent, namely the current from the solar photosphere to a filament and that from the filament to the solar photosphere on the current filament are taken into account while deducing the equation. Then relation between the current filament in the active region NOAA 131 and its balance altitude is investigated according to the equation. The result obtained shows that when a filament rises, it may be bent into a "U" shape, which is clearly in contrast with observations. It is concluded that an elliptic circuit should be closer to the real filament than the rectangular circint.