China devalue its currency because the yuan has been rising even when market forces say it should be falling. Worried Chinese have been moving money out of the country, putting downward pressure on the yuan. Yet the yuan has remained up anyway because of its link to the dollar, which has been rising. An overvalued yuan has hurt Chinese exporters by making their products more expensive overseas.
For the most part, China has recently actually wanted its currency to steadily rise, for political reasons and to keep capital from flowing out of China. China’s domestic and international goals align with a stronger yuan. That helps explain why presidential candidates like Trump haven’t been spouting off about China’s currency management as much of late.
A currency devaluation of yuan helps countries sell more exports, boosting the economy and help its own manufacturers .Right now the Chinese economy is in the midst of an economic slowdown and has suffered from stock market turmoil, so it can use some extra help. and Chinese devaluation have affect to other countries such as US exports.
the yuan gets cheaper from the perspective of American consumers, the dollar gets more expensive from the perspective of Chinese consumers. That means it's getting more expensive for Chinese people to import American-made goods, so they're likely to import fewer of them. Lower demand for US goods could mean slightly slower economic growth here in the US.