1. A nonlinear conversion method using precision mapping, comprising: receiving an input value; converting the input value into a source value and generating a preserved information by a source value converter; mapping the source value to a destination value in a limited domain for restricting the calculation within a destination domain by mapping table unit; obtaining recovering parameter according to the preserved information by a recovering parameter unit; and outputting the destination value according to the mapping table, combining the destination value with a recovering parameter for recovering an output value produced by the nonlinear conversion of the input value by an output computing unit.