A novel triplexer chip based on an asymmetric Y branch waveguide and a multimode interference is presented in this paper. Using the novel triplexer chip, a 1310nm channel is multiplexed and 1490nm and 1550nm channels are demultiplexed for FTTH using. The asymmetric Y branch waveguide is used to separate the 1310nm channel from the 1490nm and 1550nm channels. Then the multimode interference is used to demultiplex the 1490nm from 1550nm channel. The simulated spectra show the bandwidths of three response wavelengths are 100nm, 20nm and 10nm, respectively, which can meet the demand of ITU.984 completely. The isolation for 1310nm is more than 48dB, and the isolation between 1490nm and 1550nm is more than 37dB.