Abstract: The far-field of an antenna under test (AUT) is very important for studying the radiation characteristics of AUT, and the near-field measurement techniques are widely applied because the techniques can avoid direct measurement of far-field. However, the conventional near-field measurement technology requires the acquisition of the amplitude and phase distribution in near-field. Nevertheless, owing to various factors, it is becoming increasingly difficult to obtain the accurate phase information in near-field with the rise in frequency, especially at millimeter wave and sub-millimeter frequency ranges. To solve this problem, we propose a method of near-field measurement using amplitude-only data to reconstruct or guess the spherical tangential electric field distribution enclosing the AUT from the amplitude-only data over a closely complete surface. The electric field exploiting genetic algorithm (GA) for global optimization is originally derived from four random initial estimation of field distributions and will gradually approximate to the exact value during iterations. The simulation results show that combining the phase-free near-field measurement technology and genetic algorithm optimization can calculate accurate far-field radiation characteristics under the premise of ignoring the phase signal.