diff --git a/src/Common.css b/src/Common.css
index 0faa01c..2ffd30d 100644
--- a/src/Common.css
+++ b/src/Common.css
@@ -15,6 +15,20 @@
   opacity: 0.65;
 }
 
+body::after {
+  content: '';
+  position: fixed;
+  inset: 0;
+  z-index: 9999;
+  pointer-events: none;
+  background-image: url('images/watermark.svg');
+  background-repeat: repeat;
+}
+
+body.root-dark-mode::after {
+  filter: invert(1);
+}
+
 .black-outline {
   text-shadow: /* also change .flow-item-row-with-prompt:hover::before */
     -1px -1px 0 rgba(0, 0, 0, 0.6),
diff --git a/src/images/watermark.svg b/src/images/watermark.svg
new file mode 100644
index 0000000..9ef2adb
--- /dev/null
+++ b/src/images/watermark.svg
@@ -0,0 +1,5 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="240" height="140" viewBox="0 0 240 140">
+  <g transform="translate(120 70) rotate(-45)">
+    <text x="0" y="0" text-anchor="middle" dominant-baseline="middle" font-size="48" fill="rgba(0,0,0,0.016)" font-family="sans-serif">请勿截屏</text>
+  </g>
+</svg>