Using phase balance design method and the accumulating integral method, the Binary Optical Microlenses (BOML) is designed and used in high density grating wavelength division multiplexers with the working wavelength of 1.536～1.564 μm and the channel spacing of 4 nm. The phase structure of the binary optical microlenses and the diffraction far field distribution at the end of the receiving fibers are calculated. The loss resulted from the microlenses when the single mode and the multi mode receiving fiber are used, and the ratio of the fundamental modes excited in the multi mode receiving fiber for eight channels are discussed.