A multimode interference (MMI) coupler with the exponentially tapered multimode waveguide is proposed in order to reduce the scale of the MMI device. The relation between the length of the multimode waveguide and the parameters of the tapered structure was analyzed in theory. Compared with the parabolically tapered structure,which has been successfully used in the MMI devices,this structure could further reduce the length of the MMI devices. The results of the simulation by the wide-angle finite difference beam propagation method (FD-BPM) for some MMI couplers with different parameters were given. It was shown that the performance of the MMI couplers with the exponentially tapered structure was similar to the devices with the parabolically tapered structure. As a result,the exponentially tapered structure can be used in MMI devices to reduce the length of this kind of devices.