Google's contracts with large Chinese advertising resellers will end on 27 October, the company has announced.
In September Google said it would end the contracts, but has not given a reason for the decision.
It is thought the move will benefit China's leading search engine Baidu, which has more than 70% of the country's search market revenue.
This follows figures from research firm Analysys which found that Google's share of China's online market fell to 24.2% in the three months to June, from 30.9% in the first quarter.
China renewed Google's licence in July, after the web giant threatened to close its operations because of concerns about state censorship
The renewal came after the firm set up a new landing page at google.cn with links to its uncensored Hong Kong search engine.