Abstract: HIRFL beam (₁₂C⁶⁺) emittance has been measured with "Three-Profile Method" in which the beam sizes at three different locations in a field -free drift space are measured by three secondary emission multi - wire profile monitors. Measurement results are presented here. Particular emphasis has been laid on the calculations and discussions relating theoretical error of emittance measurements with the separation of the three profile monitors, the location and size of the beam waist so that the optimum conditions of emittance measurements could be determined.