When I insert new section in word 2007, I choose insert section in same page and continuos, But it adds one page, Why?
Do you mean page break? I’m not sure exactly what you’re doing because there’s no “insert section” in the insert tab. 
Insert a section break; On the ‘Page Layout tab’, in the ‘Page Setup group’, click ‘Breaks’ and pick the appropriate one.
I suspect you accidentally chose ‘Next page’ instead of: ‘Continuous’ and that would explain the extra page - I assume you actually highlighted the text in the first place?
Also if the text would fill most of the page it may inevitably shift the text onto another page anyway.