Abstract: Based on field test data,average acoustic velocity in the first ten oil-well tubings of several pumping wells is calculated.Using curve fitting,an expression for the law of changes in sound velocity inside the pumping well′s casing is obtained,which is verified with field test data obtained in a certain pumping well of the region.By using this fitted expression,sound velocity at any position in the pumping well′s casing can be calculated.The above result confirms that the law of changes in sound velocity of this region is essentially consisten.This can provide possibility for accurately determining the fluid level of pumping wells in the region.In addition,distribution of sound velocity in different pumping wells is discussed.