Countless sports celebrities showappear on the TV, and attend many social activities, they work more than training, and they get their pays incredibly higher than common people working in other professions .
--> break this into two seperate sentences. The second sentence begins from "They work more...".
Many thought it is too unfair, they, like Byrant Kobe and David Beckham, just do some training and get the opportunity to shine, it seems like esay, and how can they get so much benefits?
--> This sentence sounds like spoken language, not the academic language that you should use in TOEFL.
the reasons will be strengthened
In the introduction, you should paraphrase the topic and state your point of view. Don't ramble. For example, you don't need to give an example of Byrant Kobe and David Beckham in the intro.
Notable swimmer Micael Phelps, who won countlessnumerous gold medal and world records, trained in swimming since 6, admittedly, .heHe has great talent-his dolphin-like body shape, the slim arms and legs, buthoweverunlike our ordinaries , he works not only based on his talent, but also his stringent training which can not be accepted by us .
--> you just used "countless" previously, so don't repeat yourself. What do you mean by the greened part?
Try to write short and easy to understand sentences. Long sentences tend to make readers lost in your ideas, it might be hard to catch up with your points.
Keep on working and you'll get better.
Best