If you go by the press release from the meeting, it sums up China's main points against the draft resolution:
Zhang Jun (China) said that the United States’ draft was put forth on Saturday and included divisive elements that went beyond the humanitarian realm. His delegation, along with the Russian Federation, Brazil and the United Arab Emirates, had proposed suggestions, but these were ignored in favour of cosmetic changes. The resulting draft was “out of balance” and evasive on the urgent issue of ending the fighting, he said.
You can also watch the full statement in explanation of the vote at the Security Council by China's representative here (starts at the 19 min mark). To pick out a few main points;
On Saturday evening, the US introduced a new draft text that set aside the consensus of the members and included many elements that were skewed, deeply divisive, and that went far beyond the humanitarian realm. Several members, including China, Russia, UAE and Brazil proposed amendments to the text, however the proponent ignored the major concerns of all parties and made only cosmetic changes to the draft.
What we oppose is that the draft resolution is evasive on the most urgent issue of ending the fighting and that it has never been able to call for an immediate ceasefire in clear and unambiguous terms and at this moment ceasefire is not only a diplomatic term, it means the life or death of many civilians. If a resolution from the security council is ambiguous on the issue of war and peace, it's irresponsible and also extremely dangerous. It is tantamount to paving the way for large scale military action and giving the green light to further escalation of the war.
What we oppose is that the draft text does not call on the parties concerned to stop the indiscriminate and asymmetrical use of force, nor does it call for a thorough investigation into the heinous attack on the Al Ahli hospital. Such selective application of international law and double standards will only push more innocent civilians to the brink of death.
What we oppose is that the draft text attempts to establish a new narrative on the Palestinian-Israeli issue, ignoring the fact that the Palestinian Territories have been occupied for a long time, and evading the fundamental issue of independent statehood for the Palestinian people. It's worth being vigilant that the draft departs from the spirit of previous UN resolution and embeds the dangerous logic of confrontation of civilisations and the justification of war and the use of force. If the draft is adopted, it will completely dash the prospect of the realisation of the two-state solution and plunge the Palestinian and Israeli people into a vicious cycle of hatred and confrontation.