which difference we apply the patent first in US not in China?

“By the way, you need an agency to act for you if you want to apply US patent. It\'s essential.”
you are wrong, we can apply a us patent directly,there is no need to apply it through the patent agent department

Acording to the Chinese patent law,  an invention which was finished in China, should be first filed in China. Am I right?

I heard that \"first to invent\" rule only applys to an invention made in US, someone can confirm?

Although Chinese Patent Law requires Chinese inventors to hiring a Chinese
designated agancy to file patent application aboard, USPTO has no such requirement. An inventor can file patent application itself. However, if you do want to hire an agent, you must hire a US agent (or a Canadian ganet for special case).