Abstract: In this paper we first present an open-type microwave filter by using left handed medium (LHM). LHM is an artifial material with premittivity and permcability both negative within certain microwave frequency band. By utilizing the special characteristics of LHM, we summarize a method of design a microwave band -pass filter and give a design example of 9.90-10.1 GHz band-pass filter, this filter has excellent characteristics much better than the ordinary material can achieved.