2.) When McDonald’s opened its first store in China in 1990, their rival KFC had already been there for three years.
Don’t forget to put commas in! It should say, “…their rival, KFC, had…”

3.) It is estimated that 1.900 KFC stores are opened in China, which is more than twice as many as the Golden Arches (McDonald’s).
The word “opened” should not be past tense, if you are talking about the current time period. The phrase, “…is more than twice as many as the Golden Arches” could be rephrased to something like, “…is more than than twice the amount of the Golden…”

4.) Besides KFC, McDonald’s has other competitions in China, such as Mom and Pop food stands.
Using “competition” does not fit the sentence the way it’s written, it should say “competitors.”

5.) These businesses are usually owned by the same family generations in a single location , and their food are considered as traditional, convenient and cheap.
There’s a few parts of this sentence that don’t sound right. Here’s a better way to write the sentence: “These businesses are usually owned by the same family for many generations in a single location and their food is considered traditional, convenient and cheap.”

6.) Furthermore, the sanitation in China is another major issue for the McDonald’s.
This sentence is good except for the “the” in front of McDonald’s.

7.) China is still considered as a developing country, and its food safety is a nightmarish problem where corruption is rampant and safe food handling practices are in doubt.
You don’t need to have “as” in the first part. The last part, “…and safe food handling practices are in doubt.” needs to be changed. You could say, “… safe food handling is not always practiced.”

8.) Moreover, because McDonald’s is one of the major sponsors of the 2008 Olympics in Beijing, they want to provide customers a hygienic environment with sanitized meals.
Reword the last part, “…they want to provide customers meals made in a hygienic environment.”