When I use longtable, the table can't fit the whole text, is there any solution? Or is there a suitable way to change the page?

You have to add a pagebreak from time to time.

documentclass{article}
usepackage{longtable,lipsum}
begin{document}

begin{longtable}{|l|c|c|c|c|c|}
    hline
    multicolumn{6}{|p{10cm}|}{1. lipsum[1-4] }  hline
    pagebreak
    hline
    multicolumn{6}{|p{10cm}|}{5. lipsum[5-8] }  hline
end{longtable}

end{document}

With longtable you can run headers and footers that link the partial tables page by page.

documentclass{article}
usepackage{longtable,lipsum}

begin{document}

begin{longtable}{|l|c|c|c|c|c|}        
    hline      
    multicolumn{6}{|p{10cm}|}{Large Main heading }  
    hline
    endfirsthead
    
    multicolumn{3}{l} {footnotesize emph{ ldots{} from previous page.}} 
    hline
    multicolumn{6}{|p{10cm}|}{ Large Main heading }  
    hline
    endhead
    
    multicolumn{6}{r}{footnotesize emph{to be continued in the next page ldots{} }}  
    endfoot            

    endlastfoot            

    multicolumn{6}{|p{10cm}|}{1. lipsum[1-4] }  hline
    pagebreak
    multicolumn{6}{|p{10cm}|}{5. lipsum[5-8] }  hline
end{longtable}

end{document}