The US and other Western powers have sought to pressure Sudan into accepting UN peacekeepers to quell violence in its western province of Darfur.
But China, which buys much of Sudan's oil and wields veto-power over UN resolutions, has rejected UN forces without Khartoum's agreement.
Xinhua reported that Cao told Gaili: "Military relations between China and Sudan have been developing smoothly for a long time."
Haj Ahmed El Gaili arrived in Beijing on Sunday for an eight-day visit to China, Xinhua said.
US pressure
In Darfur, more than 200,000 people are believed to have died and about 2.5 million have been driven from their homes into squalid camps since ethnic tensions erupted into revolt in 2003.
UN reports on Darfur have blamed Arab militias, which they say are backed by Khartoum, for atrocities including mass rape and murder.
The US has pushed China to use its influence to help press Sudan to let UN peacekeepers deploy in Darfur.
Beijing says it favours a no-strings approach to investment and aid in Africa and has blocked Security Council resolutions critical of Khartoum.
Sudan is the biggest target for Chinese investment in Africa, a UN agency reported last week.