Chinese Foreign Ministry spokesman Hong Lei said Washington had briefed Beijing over the matter and China was highly concerned about any use of chemical weapons.
But he said China opposed the U.S. acting alone and believed any response must conform to the U.N. Charter and the basic principles underlying international relations.
"China ... holds the belief that a political resolution is the only realistic way to solve the Syrian issue," Hong told reporters at a regularly scheduled briefing.
"China is highly concerned about the relevant country's plan on taking unilateral military action," Hong said, adding that the international community must "avoid complicating the Syrian issue and dragging the Middle East down into further disaster."
China has consistently joined Russia in blocking any U.N. action that could lead to the downfall of Syrian President Bashar Assad's government.
The U.S. says the use of chemical weapons in Syria killed at least 1,429 civilians. The U.S. argues that Assad's government is responsible, while others say the evidence is not clear.
President Barack Obama is trying to convince Americans and the world about the need for action in response to the attack. Only France is firmly on board among the major military powers, after Britain's Parliament rejected the use of force in a vote last week.
Russia's foreign minister, Sergey Lavrov, said Monday the information the U.S. showed Moscow to prove the Syrian regime was behind the chemical attack was "absolutely unconvincing."
Hong didn't address the possibility of the U.S. acting together with France or another ally, although Beijing would almost certainly be opposed to any action.