A compact and robust frequency-doubled telecom laser system at 780nm is presented for a rubidium cold atom interferometer using optical lattices. Adopting an optical switch at 1.5µm and a dual-wavelength second harmonic generation system, only one laser amplifier is required for the laser system. Our system delivers a 900mW laser beam with a detuning of 110GHz for the optical lattice and a 650mW laser beam with an adjustable detuning between 0 and −1GHz for the laser cooling, the detection and the Raman transitions.