I have one text that need to be italicized.
\textit{some text2 ~\\ some text2}
But i found ~\\ converted to \newline\. Is there any alternative to \textit? Is there any alternative to \it?
I assume your intent was to get a backslash, instead of a \newline which is what \\ is. In that case you can use \textbackslash with either the macro \textit{...}, or the font switch {\itshape ...} as in the first two lines below:

The third line above was produced with \emph{...} and yields identical results (in this case).
However, you should carefully consider why you are doing this. Do you want an italic font, or are you trying to emphasize some words? In most cases one is trying to emphasize some words in which case \emph{...} should be used. Note the differences in the following where we have nested uses of \textit{...}, {\itshape ...}, and \emph{...}:

{ and } when using the switch \itshape is so that the italics font switch is only on during within a scope.\documentclass{article}
\begin{document}
\textit{some text2 ~\textbackslash~ some text2}
{\itshape some text2 ~\textbackslash~ some text2}
\emph{some text2 ~\textbackslash~ some text2}
\medskip
\textit{textit text containing \textit{textit text}}
{\itshape itshape text containing {\itshape itshape text}}
\emph{emphasized text containing \emph{emphasized text}}
\end{document}
\newlinein this context. – Franck Pastor Apr 10 '14 at 09:21\\. – Ruben Apr 10 '14 at 09:24\textitwhen they really need\emph. Why do you want to typeset text in italics? – Apr 10 '14 at 09:31~\\”, obviously, all the text inside\textit{…}will be italicized. By the way, I would normally use\emphinstead of\textitas Marc van Dongen said. – Manuel Apr 11 '14 at 10:38\\should provide you with the character that\textbackslashwould offer? – wasteofspace Jun 16 '14 at 12:41