In order to realize the miniaturization and multi-function of optoelectronic devices and further improve the capacity and speed of information transmission, an on-chip integrated device based on photonic crystal for dual-wavelength electro-optic modulation and mode division multiplexing (MDM) is proposed. The electro-optical modulation module of the integrated device is composed of a silicon-based photonic crystal waveguide and two L3 composite resonators, and the MDM module consists of silicon-based asymmetric parallel nanowire waveguides. A silicon-based photonic crystal waveguide is used at the junction of the two modules. The L3 composite resonators and PN doping structure are used to achieve the modulation of the two-wavelength TE₀ mode, and the asymmetric directional coupling structure is used to convert the TE₀ mode of two wavelengths into the TE₁ mode. The parameters of the integrated device are calculated using three-dimensional finite-difference time-domain (3D-FDTD) method. The results show that when the voltage is 1.05 V, the integrated device can achieve a center wavelength of 1 552.1 nm and 1 556.1 nm TE₀ mode, TE₁ mode on-off modulation and two-mode mode division multiplexing function. The extinction ratio of the device is as high as 24.67 dB, and the modulation depths are both 0.99. The insertion loss and the channel crosstalk are less than 0.57 dB and -34.68 dB, respectively. And the minimum modulation speed is 17.54 GHz. The integrated device has compact structure and is expected to be applied to high-speed and large-capacity optical communication systems.