The process of mass transfer in nano-fluids was simulated by using lattice Boltzmann method based on two different ways，one is based on the finite volume of a particle method and the other is based on the point source of particles method.In those methods，the modified Boltzmann equation and the equation of mass diffusion coefficient in nano-fluids was given，moreover，the numerical results were compared with Xuan Yimin’s experimental data.Finally，the mass diffusion coefficient of CO2 in nano-fluids were calculated，the results show that the micro-perturbation of nano-particles greatly enhanced on the mass transfer，provide a new way for CO2 absorption，and proved that the reason of enhancement of mass transfer in nano-fluid is mainly relied on the convective mass transfer that was caused by the micro-perturbation of nano-particles.