Abstract: Using Lattice Boltzmann method on GPU, viscous fingering of chemical fluids in porous media is simulated at pore scale. Influence of chemical reaction on fluid mixing is quantified. A one-variable chemical model admitting two stable states is adopted and a homogeneous artificial medium is generated by Quartet Structure Generation Set (QSGS) method. It shows that chemical reaction makes fingering interfaces sharp, restrains fluid mixing, and causes demixing. Influence is enhanced with increase of chemical reaction rate.