The Pew Charitable Trusts report on clean energy found that China attracted $65.1 billion in renewable energy investment, the third time the country has headed the investment rankings since 2009.
The report said investment levels worldwide declined 11 percent during the year.
The United States, last year's world leader, ranked second with investment in the sector dropping 37 percent to $35.6 billion in 2012.
Germany ranked third with $22.8 billion, down 27 percent compared with the previous year.
"When we look around the world, we see policy really matters when it comes to where investment will be going," said Phyllis Cuttino, director of Pew's Clean Energy Program.
She added that renewable energy investment policies in the US have been very uncertain, meaning investors have looked elsewhere, in areas where returns can be more guaranteed.
The assessment report showed the center of gravity for investment has shifted from the traditional, established markets in the West to emerging markets in the East.
Investment in the Asia and Oceania region grew by 16 percent to $101 billion in 2012, making it the leading regional destination for investment for the first time.
Apart from rapid growth in China, clean energy investment in Japan soared 75 percent in 2012, thanks to national efforts to develop alternatives to nuclear energy after the Fukushima Daiichi nuclear disaster in 2011.
South Africa, meanwhile, emerged as the fastest-growing destination for clean energy investment among the G20 nations after attracting $5.5 billion, from less than $100 million in previous years.
"More money will be going into South Africa, as long as it keeps its policies in place," said Cuttino, who added that the country has put some ambitious targets and policies in place, such as its renewable energy tender program to encourage development of the sector.
Although worldwide investment in the sector fell last year, reached new generating capacity installed in 2012 hit a record 88 gigawatts, said the report.
China accounted for 30 percent of total clean energy investment in the G20 nations during the year, adding 23 gW of capacity, which accounted for 25 percent of the newly installed clean energy in the whole year, the report showed.
Cuttino said a sustained decline in the price of clean energy technologies and economies of scale had led to lower costs.
Lin Boqiang, director of the Center for Energy Economics Research at Xiamen University, said investment in clean energy often comes with a lag, and the record installed capacity might also be a delayed benefit of investments from previous years.
According to an earlier Bloomberg New Energy Finance report, clean energy investment slid 22 percent worldwide in the first quarter of 2013.
Investment in renewable and energy-efficiency technologies in the US fell 54 percent to $4.5 billion, while investment in China declined 15 percent to $8.8 billion during the period.
"Each year the first quarter is generally down, although is not down this much. This was the worst first quarter since 2009. As the economy improves, I think the market is pretty resilient," added Cuttino.
Lin said: "China has little problem in keeping a 30 percent annual growth in clean energy investment, largely due to a relatively low base.
"Also, the government has taken more action to help struggling manufacturers survive."
Established in 1948, The Pew Charitable Trusts is an independent US-based non-profit non-governmental research and public policy organization.