diff --git a/runtime/processor/wetext_processor.cc b/runtime/processor/wetext_processor.cc
index 1027a82..e30d117 100644
--- a/runtime/processor/wetext_processor.cc
+++ b/runtime/processor/wetext_processor.cc
@@ -15,8 +15,49 @@
 #include "processor/wetext_processor.h"
 
 #include "utils/wetext_log.h"
+#include "utils/wetext_string.h"
 
 namespace wetext {
+
+static char32_t UTF8ToCodePoint(const std::string& ch) {
+  int len = UTF8CharLength(ch[0]);
+  char32_t cp = 0;
+  if (len == 1) {
+    cp = static_cast<unsigned char>(ch[0]);
+  } else if (len == 2) {
+    cp = ((static_cast<unsigned char>(ch[0]) & 0x1F) << 6) |
+         (static_cast<unsigned char>(ch[1]) & 0x3F);
+  } else if (len == 3) {
+    cp = ((static_cast<unsigned char>(ch[0]) & 0x0F) << 12) |
+         ((static_cast<unsigned char>(ch[1]) & 0x3F) << 6) |
+         (static_cast<unsigned char>(ch[2]) & 0x3F);
+  } else if (len == 4) {
+    cp = ((static_cast<unsigned char>(ch[0]) & 0x07) << 18) |
+         ((static_cast<unsigned char>(ch[1]) & 0x3F) << 12) |
+         ((static_cast<unsigned char>(ch[2]) & 0x3F) << 6) |
+         (static_cast<unsigned char>(ch[3]) & 0x3F);
+  }
+  return cp;
+}
+
+static bool IsKnownChar(char32_t cp) {
+  // ASCII printable characters (space to ~)
+  if (cp >= 0x0020 && cp <= 0x007E) return true;
+  // CJK Unified Ideographs
+  if (cp >= 0x4E00 && cp <= 0x9FFF) return true;
+  // CJK Unified Ideographs Extension A
+  if (cp >= 0x3400 && cp <= 0x4DBF) return true;
+  // CJK Compatibility Ideographs
+  if (cp >= 0xF900 && cp <= 0xFAFF) return true;
+  // CJK Symbols and Punctuation
+  if (cp >= 0x3000 && cp <= 0x303F) return true;
+  // General Punctuation
+  if (cp >= 0x2000 && cp <= 0x206F) return true;
+  // Fullwidth forms
+  if (cp >= 0xFF00 && cp <= 0xFFEF) return true;
+  return false;
+}
+
 Processor::Processor(const std::string& tagger_path,
                      const std::string& verbalizer_path) {
   tagger_.reset(StdVectorFst::Read(tagger_path));
@@ -76,8 +117,28 @@ std::string Processor::Verbalize(const std::string& input) {
   return output;
 }
 
+std::string Processor::TagOOV(const std::string& input) {
+  std::vector<std::string> chars;
+  SplitUTF8StringToChars(input, &chars);
+  std::string output;
+  for (const auto& ch : chars) {
+    char32_t cp = UTF8ToCodePoint(ch);
+    if (IsKnownChar(cp)) {
+      output += ch;
+    } else {
+      output += "<oov>" + ch + "</oov>";
+    }
+  }
+  return output;
+}
+
 std::string Processor::Normalize(const std::string& input) {
-  return Verbalize(Tag(input));
+  std::string output = Verbalize(Tag(input));
+  if (parse_type_ == ParseType::kZH_TN &&
+      output.find("<oov>") == std::string::npos) {
+    output = TagOOV(output);
+  }
+  return output;
 }
 
 }  // namespace wetext
diff --git a/runtime/processor/wetext_processor.h b/runtime/processor/wetext_processor.h
index e11d307..78da511 100644
--- a/runtime/processor/wetext_processor.h
+++ b/runtime/processor/wetext_processor.h
@@ -34,6 +34,7 @@ class Processor {
   std::string Tag(const std::string& input);
   std::string Verbalize(const std::string& input);
   std::string Normalize(const std::string& input);
+  std::string TagOOV(const std::string& input);
 
  private:
   std::string ShortestPath(const StdVectorFst& lattice);