回複：請教一個跨國征稅的問題

美國政府全球征收所的稅這一塊兒 ，是否涉及房產 增值了？我搜了一下，好象沒有發現房產的說法。

Yes, you have to pay capital gain tax on the gains in China.  You are supposed to report the Chinese property.  IRS might not go look for it, but if someone told IRS you hid somehting, they'll come after you.
 

另外 ，裝修這 一塊兒的花費，是否可以加到原始房價中？
Yes。Improvement cost can be added to the cost basis.

如果用國內的房款所得，還美國的房屋貸款，是否可以避稅？

No.  You have to pay US capital gain tax on chinese gain.  There is a 1031 exchange, but it has very stringent rules and it is not as simple as you said.

那個法律文件可以查到這樣的信息？

I recommend you talk to an accountant.  Whatever you read is only partial information.  盲人摸象。