Multiple wavelength DFB laser array and multimode interference coupler integrated light source device has important application prospect in the dense wavelength division multiplexing system. A strongly guided InP/InGaAsP multimode interference coupler is designed and simulated by using 3D FD-BPM method in order to research the optical coupler used in the broadband available multiple wavelength integrated light source. Tapered input/output waveguides are used to reduce the insertion loss of the multimode interference coupler and to improve the uniformity of the output ports. Combined with the metal organic chemical vapor deposition (MOCVD) epitaxial growth apparatus and according to the simulation results, a 1-by-4 multimode interference coupler is fabricated by using reactive ion etching process. The insertion loss and the uniformity of the device is measured by automatic alignment waveguide coupling test system. The test result shows that the device has 40nm available bandwidth and 2.6dB pass band flatness around 1550nm.Furthermore, the insertion loss is no higher than 10dB at the designed wavelength 1550nm.