documentclass{article}
usepackage[margin=1in]{geometry}
usepackage{multirow,tabularx}
newcolumntype{Y}{>{centeringarraybackslash}X}
renewcommand{arraystretch}{2}
begin{document}pagestyle{empty}
begin{tabularx}{textwidth}{|*{4}{Y|}}
hline
multirow{2 }{*}{textbf{Similarity}}
  &  multicolumn{2}{c|}{textbf{RMSE}}  & \
cline{2-4}
             &   Movielens        & Movielens  \
hline
Cosine &         0.9345                &0.9345         \
hline
Pearson    &      0.9345               &0.9345       \ hline
end{tabularx}
end{document}