I take it you mean a military stand whereby China commits military force to defend Iran against the US.
Only under one set of circumstances can I imagine China committing troops. It would be part of a prior decision by China to go to war over Taiwan.
But, I don't think China needs to commit troops to make a stand with Iran. What I think they're doing is providing technology and weapons and providing strategic and tactical planning assistance. You can bet they've made a close study of Gulf War I, Yugoslavia, Afghanistan, and Gulf War II. They've probably got a lot of (theoretical) knowledge to sell the Iranians.
The Chinese military doesn't exactly have a glorious military record, anyway. They're still flushing crimson at the humiliation handed them by the Vietnamese. And, their general officers have acknowledged at various times, recently, that they cannot win a conventional war with the US. So, that brings us back to Taiwan, I think, and the prospect of nuclear war.
Now, should Russia and China accept Iran's request to join the Shanghai Cooperation Organization, that might signal something as dangerous as Taiwan.
But does China have the internal security and the nationalist fervor to face the consequences of a real war? I tend to think they do not.
Taiwan, as a factor of square miles, isn't much. And if China were to take over Taiwan, and change Taiwan's ways to China's bizarre interpretation of capitalism, Taiwan would cease to be a magic generator of wealth. (China understand production better than the West in some ways, but they don't have a clue about "wealth" -- wealth in the Henry Ford tradition. And that's a cultural byproduct of The Little Red Book)
If some Islamic country wanted to take over a wildly popular beach resort - and when they did, they separated men and women and only allowed swimmers in the water if they were covered head to foot... It wouldn't stay "wildly popular". Same with Taiwan.