In this paper a low pass microwave filter has been designed. the filter has designed by step impedance method in which the alternative part characteristic linear imperdance is too high or too low design. in this filter with changing every high or low impedance characteristics such as length or width desired characteristics can be rich and it has simulated by using of HFSS software, and relying on full-wave analytical methods in three dimensional work page. design with making by the micro strip technology, it becomes practical. this filter has less complexity rather than others filters. result of practical measure and simulation have been a fairly good agrrement together.