The investigations on the structure, magnetic and transport properties were carried out for the double perovskite Sr2Fe1-xCoxMoO6 samples prepared by the solid state reaction method. It is found that the relationship between resistivity and temperature changes from a typical half-metal behavior to a semiconductor behavior, with the increasing substitution concentration x value of Co for Fe. The resistivity at room temperature increases from 3.9×10-5Ω·cm (for the x=0 sample) to 6.0×10-1Ω·cm (for the x=1.0 sample). The magnetic order in the sample changes from a ferrimagnetic to an antiferromagnetic and the magnetic transition temperature TN decreases with the increasing Co content x. The magnetoresistance effect is depressed by the Co partial substitution for Fe. The origin of magnetoresistance and the Co substitution effect were discussed in detail based on the analysis of electronic structure of Sr2Fe1-xCoxMoO6 system.