Evan Osnos says that getting China to lean on North Korea isn't likely:
By the morning after North Korea’s most serious artillery attack on the South in decades, the unofficial American consensus had coalesced around a clear, unsurprising, and ostensibly comforting position: “The United States and its allies should hold Beijing responsible for putting a stop to Mr. Kim’s dangerous behavior,” as the Washington Post editorial page put it. The Times agreed: “China … has the best chance of walking the North back from the brink. It must take the lead.”
Now that this is settled, there’s only one problem: China doesn’t want to take the lead, and chances are that it won’t anytime soon. Adopting that as the ultimate goal of international strategy is probably a recipe for non-action.
Greg Scoblete doesn't think China has all that much power over the Hermit kingdom:
It's possible for China to really pressure the North by cutting off aid, but, as Jian notes, fears of a refugee flood and the prospect of an American military presence directly on their border has thus far stayed China's hand.