Speaking at the Shangri-La Dialogue in Singapore, he stated that China's actions were peaceful and legitimate, warning other countries against trying to "sow discord" over the matter.
"There is no reason for people to play up this issue in the South China Sea," Sun said, adding that the creation of the ADIZ hinges on any threats to air or maritime security.
He rejected recent remarks by US Defense Secretary Ash Carter, who said that Beijing's land reclamation projects in the disputed waters around the Spratly archipelago of the South China Sea allegedly boost the risk of "miscalculation or conflict" and is out of step with international rule.
"We hope relevant countries will work together in the same direction to build the South China Sea into a sea of peace, friendship and co-operation", Sun added.
Apart from China, the Spratlys are claimed by half a dozen countries, including Malaysia, Taiwan, the Philippines and Vietnam. Neither Japan nor the United States have any territorial claims in the South China Sea.