Filter is a key part of the communication or radar systems. Considering the performance, cost and technics, a two-dimensional (2-D) photonic bandgap (PBG) metal waveguide filter based on the microelectromechani-cal systems (MEMS) is a good choice when the system works at terahertz (THz) frequencies. In this paper, a 2-D PBG metal waveguide filter with square rods structure is analyzed. The design method is given and a narrowband filter working at 0.46 THz is designed. The simulation results show the filter has a good performance. The fractional bandwidth is 4%, the rejection at one time bandwidth out of the passband is larger than 10 dB, and the insertion loss at the center frequency is −0.46 dB.