The dissipative particle dynamics simulation technique is used to study the microphase transitions of perforated lamellae of cyclic diblock copolymers under steady shear. The perforated lamellae are transformed to perfect lamellae, and the layer normal is aligned to the direction parallel to the gradient of the velocity under weak shear, whereas they undergo a phase transition to form perfect lamellae whose normal is aligned to the direction perpendicular to the gradient of the velocity due to strong shear. Subjected to the moderate shear, the perforated lamellae are transformed to hexagonally ordered cylinders. By examining the microphase morphologies in the shearing process, we find shear thinning in general, which is reflected by the reorientation of the lamellae, and shear-induced thickening when hexagonally ordered cylinders appear. The calculated shear viscosity basically decreases with increasing shear rate but shows a local maximum at the shear rate that induces hexagonally ordered cylinders.