With the rapid development of meta-materials, the requirements for the precision of measurement of the effective electromagnetic parameters become increasingly high. A research on the measurement of the effective electromagnetic parameters has been made and free-space method is presented. Compared with other methods, this free-space method is a untouchable and nondestructive test method ,and when using this method, the sample is not strictly required in shape and technology but it should be homogeneous in thickness and big enough in test area to avoid diffraction effects at the edges. An effective way is proposed for solving the multi-valued problem and phase-shift ambiguity problem in the parameter inversion process by the theoretical analysis. The effective electromagnetic parameters of air and meta-material samples are tested by using the free-space method, and in comparison with the results of the wave-guide method in the band (8 GHz-14 GHz), the results indicate that this test method is correct, reliable and practical.