The mass transfer between non-aqueous phase liquid(NAPL) phase and soil gas phase in soil vapor extraction(SVE) process has been investigated by one-dimensional venting experiments. During quasi-steady volatilization of three single-component NAPLs in a sandy soil, constant initial lumped mass transfer coefficient (lambda(gN,0)) can be obtained if the relative saturation (xi) between NAPL phase and gas phase is higher than a critical value (xi(c)), and the lumped mass transfer coefficient decreases with xi when xi < xi(c). It is also shown that the lumped mass transfer coefficient can be increased by blending porous micro-particles into the sandy soil because of the increasing of the interfacial area.