Influence of lattice constant on transmission,negative refractive index (NRI) and FOM of left-handed materials was studied.It shows that lower-order transmission peak of left-handed materials increases unusually with lattice constant decreased,due to impedance matching.And center frequency of NRI of left-handed materials is blue-shifted with decreased lattice constant,which is consistent with theoretical results.As lattice constant decreased to a certain value,perfect impedance matching is achieved which leads to higher FOM.