Abstract: By establishing the interpreting model of large pore well testing theory,a new simple and economic method of determining the existence of large pores was found involving the use of typical curve fitting,i.e.,the logarithmic curve of injection wellhead pressure drop.The pressure drop at the water injection wellhead can be described using the pressure drop equation of instable well testing,and a logarithmic curve can be drew;by fitting the curve drew with the real measured points vs different time interval and the located curve by the interpreting model,it then can be determined whether or not there are large pores.The feasibility of this method was verified in the plugging and profile control of the two units as L13-9 and L41-11.