回复：请教一个跨国征税的问题

美国政府全球征收所的税这一块儿 ，是否涉及房产 增值了？我搜了一下，好象没有发现房产的说法。

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 ，装修这 一块儿的花费，是否可以加到原始房价中？
Yes。Improvement cost can be added to the cost basis.

如果用国内的房款所得，还美国的房屋贷款，是否可以避税？

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.

那个法律文件可以查到这样的信息？

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