A non-linear interpolation circuit includes current interpolation units and an I-V converter. The current interpolation units receive an operating voltage corresponding to digital image data and corresponding reference voltages to generate corresponding operating currents. When the operating voltage changes, at least one of the corresponding current interpolation units generate the corresponding operating current, and the operating currents with respect to the operating voltage are superimposed to form an interpolation current. The I-V converter converts the interpolation current into an interpolation voltage. An interpolation current generating circuit and a method for converting digital data into analog data are also disclosed herein.