The present invention provides a paint composition including a primer and a finish paint. The primer includes a resin matrix, and a hydroxylated carbon nano-material admixed into the resin matrix. The hydroxylated carbon nano-material has a relatively high proportion of hydroxyl groups. The finish paint includes colloidal silica having a relatively high proportion of hydroxyl groups. The hydroxyl groups of the colloidal silica are capable of a dehydration reaction with the hydroxyl groups of the carbon nano-material at an interface between the primer and the finish paint. The present invention also relates to a coating structure including a priming coating and finish coating, and to a method for coating a substrate using the paint composition. The coating structure using the paint composition has good transparency and high mechanical strength.