diff --git a/figures/logo-left.png b/figures/logo-left.png
deleted file mode 100755
index 89be975..0000000
Binary files a/figures/logo-left.png and /dev/null differ
diff --git a/figures/logo.pdf b/figures/logo.pdf
new file mode 100644
index 0000000..e133f98
Binary files /dev/null and b/figures/logo.pdf differ
diff --git a/thesis.cls b/thesis.cls
index f34b893..7d80852 100644
--- a/thesis.cls
+++ b/thesis.cls
@@ -1812,7 +1812,7 @@
       \raggedleft\fangsong\fontsize{14bp}{14bp}\selectfont
       \null\ustc@secret@level\par}\par
     \vskip 0.5cm%
-    \includegraphics[height=1.3cm]{figures/logo-left.png}\par
+    \includegraphics[height=1.3cm]{figures/logo.pdf}\par
     \vskip 0.6cm%
     {\sffamily\fontsize{56bp}{56bp}\selectfont
       \ustc@thesis@name\par}%