Chinese President Hu Jintao made the announcement as he opened a summit in Beijing attended by nearly 50 African heads of state and ministers.
The summit is focusing on business with more than 2,000 deals under discussion.
African leaders welcome their booming trade links with China, but critics accuse Beijing of dealing with repressive regimes.
Beijing says it is just doing business and has no political agenda.
"Our meeting today will go down in history," Mr Hu told the China-Africa summit.
"China will forever be a good friend, good partner, good brother of Africa," he said.
Ethiopian Prime Minister Meles Zenawi remembered China's support during many African countries' fight for independence.
"Our main challenge now is not to fight colonialism, but fighting poverty and backwardness and achieving economic independence," Mr Zenawi said.
"Africa needs the support of its friends to overcome this challenge."
The city has been smartened up for the arrival of the African leaders, the BBC's correspondent Daniel Griffiths in Beijing says. Red lanterns hang from trees and posters celebrate Sino-African friendship.
Mr Hu said that China would double its aid to Africa from its 2006 level by 2009, although he gave no figures.
Beijing will offer US$3bn (£1.5bn) in preferential loans and US$2bn (£1.5bn) in export credits over the next three years, President Hu said.
It will more than double the number of goods which do not attract tax when imported to China from Africa.
China will train 15,000 African professionals and set up a development fund to help build schools and hospitals.
China's drive to buy African oil and other commodities has led to a big increase in two-way trade, worth $42bn (£22bn) in 2005.
Africa is also a growing market for Chinese goods, but critics say Beijing is stifling African manufacturing.
Some analysts have said Africa is the only place left to go, as most of the world's other big oil reserves are already being developed by major Western energy companies.
The three-day summit is concentrating on the rapidly expanding economic ties between the two sides, and many new business deals are likely to be announced over the weekend.
Many of them are expected to revolve around China's hunger for African mineral resources, particularly oil.
Some critics have voiced concerns over how Chinese-owned firms treat African workers.
Protests broke out in Zambia in July about the alleged ill-treatment of workers at a Chinese-owned mine, and there have been reports of pay disputes in Namibia.
Human Rights Watch said that all powers involved in Africa, including China, should place human rights at the centre of their policies.
"Africans do not need another external power enabling abusive regimes," the group said in a statement on Saturday.
Many economists argue that overall, China's growing economic ties to Africa are benefiting the region.
Source: BBCGüncelleme Tarihi: 20 Eylül 2018, 18:16