i like to know if there is any way to decrypt a plain-text that is encrypted 55 rounds using Caesar ciphers with different key for each round. and using brute force attack without knowing the length of the keys and character used
An encrypted plain-text is a cipher-text. A Plain-text - like its name says - is an unencrypted text.
The Caesar cipher is a simple encryption in which every plain-text letter of a given string is shifted by a given key.
Like schroeder said, your question looks awfully specific and it seems to be a homework question.
Anyway: If you rotate a given string 55 rounds with a different key (e.g. 1-26 for the latin character set), at the end there is only one single key to decrypt the whole cipher-text to a meaningful plain-text which doesn't looks like garbage. That is simply because the function is nothing less or more than:
encrypt(encrypt(encrypt(encrypt(string,key1), key2), key3), keyx)
The algorithm uses the output of the first round as input for the second round and so on. If one knows the cipher-text and the plain-text he doesn't need to reproduce all X rounds. He simply is able to figure out one key from cipher-text to plain-text. If one only knows the cipher-text, a analysis of the quantity of every letter in the alphabet in known words would help to guess this one key. A simple explanation of this you can find here:
I hope, that this "answer" helps you to put a little bit effort in solving your specific 55-Round encryption problem.