"China is firmly opposed to Japan's relevant actions," Defense Ministry spokesman Geng Yansheng said in a statement.
Earlier this week, Japan approved its first national security strategy, which implements new military program guidelines and a defense buildup plan, Xinhua reported.
Japan also plans to purchase F-35 stealth fighters, submarines, a surveillance drone fleet and 17 Boeing Osprey aircraft, the BBC reported.
Geng argued that Japan is using the pretext of its national security in order to expand.
"We urged Japan to make deep introspection on its history, honor its commitment to peaceful development, and try to improve its relations with Asian neighbors with concrete actions, so as to play a constructive role in safeguarding regional peace and stability," Geng said.
His comments come during a conflict between the two countries over two islands in the East China Sea.
Japan ranks fifth in the world in military spending, while China ranks second behind the United States, the Stockholm International Peace Research Institute said.