4. i want to use loop for read 300 number from table but i don't do it because at89c51 have register 8 bit"

Of course it does - that's why it's called an 8-bit processor!

If you want to do 16-bit (or more) arithmetic, you will have to program it yourself using the available 8-bit registers and 8-bit instructions!
Take a look at the Code Library for examples.