The pipeline will carry 30 billion cubic metres of natural gas a year from the Central Asian nation, Dow Jones Newswires reported on Wednesday.
The source said the pipeline's cost would run into tens of billions of dollars.
The report said the project would also double the capacity of an existing pipeline that carries gas from the Xinjiang region of China's northwest to Shanghai on the east coast.
The pipeline would have to go through either Kazakhstan or a combination of Tajikistan, Uzbekistan and Kyrgystan.
China signed a deal in April to buy gas from Turkmenistan, but did not release price details.
China is trying to expand its use of natural gas to reduce its reliance on oil and coal.
It is also holding talks with Russia on plans to construct a pipeline to deliver Siberian gas to northern China.
Last week, 130 companies from 26 different countries attended a two-day oil and gas conference in Ashgabat, Turkmenistan's capital.