A metal-dielectric-metal (MDM) filter is designed which is composed of a slot cavity and two waveguides. The influence of main structure parameters on the transmission characteristics of the filter is analyzed in detail using the finite-difference time-domain (FDTD) method. It is found that the lateral displacement L_d has a significant impact on transmission properties of the filter,which will lead to the appearance of new resonance peaks. In addition, it is shown that the increase of the cavity width W_c will not only make the number of transmission peaks increase, but also make the transmission peaks distribute more uniformly in the range from 600 nm to 1500 nm within limits. Through parameter optimization, a multi-channel filter distributed near the 550, 730, 920 and 1330 nm wavelength windows in optical communication systems is designed. The design has the advantages of narrow transmission peak, good quality factor, simple structure, easy integration and easy fabrication, which can be well used in wavelength-division multiplexing system and optical communication.