Abstract: Aiming at the low utilization rate of magnesium slag and high requirement of modern concrete for dimension stability, we have designed an orthogonal test scheme to experimentally study the drying shrinkage characteristics of composite concrete mixed with magnesium slag and fly ash. Results show that the shrinkage increases with time following a trend of hyperbolic curve with a high correlation. Either magnesium slag or fly ash has inhibitory effect on shrinkage deformation and the former's effect is stronger. This inhibitory effect is enhanced when fly ash is added into magnesium slag composite. The effect of magnesium slag on drying shrinkage builds up gradually with time and tends to be stable at roughly 90 d. Only shrinkage occurred and neither expansion nor expandable harm in concrete has been observed during the testing period. Thus, it is feasible to add a certain amount of magnesium slag to compensate the shrinkage of concrete.