China's power generation total was 289.7 billion kWh in May, down 3.54 percent from a year earlier, the State Grid Corporation of China said in Beijing on Wednesday.
The decline failed earlier market expectation that the country's power output was to recover soon. April's fall had been 3.55 percent.
China's power generation total has continued to fall since late 2008, signaling national economic slowdown amid global economic downturn.
Power generation tumbled 9.6 percent year-on-year in November, the biggest fall in a decade.
The rate of decline has begun to stabilize, with the year-on-year monthly fall between 3 and 4 percent since the beginning of the year, said Wang Yonggan, chief secretary of China Electricity Council.
However, it was still too early to conclude power generation has already "bottomed out", said Wang, and both power output and consumption were likely to keep falling year-on-year in the first half of 2009 before an expected increase in demand from the coastal regions kicks in.