Beijing is trying to prevent the release of a report, which says Chinese bullets have been used against Darfur peacekeepers, unnamed UN diplomats say.
The report is being discussed by a United Nations committee which monitors sanctions against Sudan, including an arms embargo on Darfur.
Beijing says it is vaguely worded and full of flaws.
Ceasefires and peace negotiations have failed to end the conflict in the volatile western Sudanese region.
The report says that a dozen different brands of Chinese bullet casings have been found in Darfur, some at sites where attacks on UN troops took place.
The BBC's Barbara Plett at the UN in New York says the allegations are controversial, but adds that China has the right to sell munitions to Khartoum as long as they are not used in Darfur.
Sudan and China are close allies - Beijing has played a key role in developing Sudan's oil industry.
The report, prepared by a panel of experts, was intended to be published after being formally presented to the UN Security Council.
The panel has previously claimed that large amounts of foreign arms and ammunition are being trafficked into Darfur and fuelling the conflict between the government and rebel groups.
After a meeting of the UN committee on Wednesday, Chinese diplomat Zhao Baogang said his government strongly objected to the report.
"Where did they get the informed sources? No evidence is given," he said, adding that the report "lacks confirmed facts".
He added: "How can we agree on those recommendations? We ask them to improve the work of the methodology."
The UN says that about 300,000 people have died and more than 2.6 million displaced by fighting since rebels took up arms in the region in 2003.
Sudan's President Omar al-Bashir is wanted by the International Criminal Court on charges his forces committed war crimes in Darfur - allegations he strongly denies.
His government says the number of casualties in the Darfur conflict has been exaggerated for political reasons and the real figure is about 10,000.