\definecolor{ublue}{rgb}{0.152,0.250,0.545}
\begin{tikzpicture}
\begin{axis}[ 
width=10cm, height=5cm, 
symbolic x coords={1-15,16-25,26-35,>35},
xtick=data,
ytick={10,12,...,28},
xlabel={句子长度（范围）},
ylabel={$\%$\footnotesize{mTER}},
xlabel style={align=center},
ylabel style={},
y tick style={opacity=0},
x tick label style={font=\small},
y tick label style={font=\small},
tick align=inside,
ymajorgrids,
major grid style={draw=ublue,dashed},
legend pos=outer north east,
legend style={anchor=north west,yshift=-1cm},
ymin=10,
ymax=28]
\addplot [sharp plot,very thick,red!60,mark=diamond*] coordinates{(1-15,11.3) (16-25,16.4) (26-35,17) (>35,19.8)};
\addplot [sharp plot,very thick,purple!60,mark=triangle*] coordinates{(1-15,14.4) (16-25,22.6) (26-35,23.8) (>35,25.9)};
\addplot [sharp plot,very thick,green!60,mark=square*] coordinates{(1-15,14.9) (16-25,23.7) (26-35,24.7) (>35,26.4)};
\addplot [sharp plot,very thick,blue!60,mark=*] coordinates{(1-15,17.5) (16-25,24) (26-35,25) (>35,27)};
\legend{\scriptsize{NMT},\scriptsize{SPB},\scriptsize{HPB},\scriptsize{PBSY}} 
\end{axis}
\end{tikzpicture}

%---------------------------------------------------------------------