When i'm reading a book i feel that i can write like it but ,if i start to write i could not write like what i read why?

Saleem I agree with Anayat, whilst reading you can "connect" with the way the book is written and have an "understanding" of what is written. However when it comes to putting your own thoughts into writing more often than not you will be unable to write in the same "vein" as the author you have been reading. Writing tends to be a very "individual" thing but don't for one minute think that you can't write purely because you feel that you are unable to match other authors! I consider myself a "reasonable" writer but could never in my wildest dreams replicate the prose of the likes of Hemingway, Dickens and other noteworthy writers - I can however equate fully to their subject matter!

Reading and writing seems to be of the same category but in fact both needs different skills to go through. In reading we need understanding of the text or comprehension but writing needs the skills of vocabulary and construction of sentences, etc. 

Although it is hard in the initial efforts but a continuous exercise improves the situation.

i have read multiple books more than once but there was one book which got my heart. The book was called Go girls angles, it was a great book based on a team of 6 girl who had one dream of WINNING their school project. They faced many challenges and went through many obstacles. This story gave me a lesson which was NEVER GIVE UP!

I'm guessing you get that feeling whenever you read the book.

 

If you're away from the book, you won't have the motivation for writing a book like it.

Simply because reading and writing are different skills that need to be developed through practice, and over the time!