diff --git a/mineru/utils/span_pre_proc.py b/mineru/utils/span_pre_proc.py
index 80fd375a..e5afc43b 100644
--- a/mineru/utils/span_pre_proc.py
+++ b/mineru/utils/span_pre_proc.py
@@ -66,10 +66,7 @@ def txt_spans_extract(pdf_page, spans, pil_img, scale, all_bboxes, all_discarded
             textpage=textpage,
             page_char_count=page_char_count,
         )
-        page_all_chars = [
-            char for char in page_chars['chars']
-            if _is_supported_rotation(char['rotation'])
-        ]
+        page_all_chars = _get_chars_for_span_fill(page_chars)
 
         # 计算所有sapn的高度的中位数
         span_height_list = []
@@ -140,6 +137,77 @@ def _is_supported_rotation(rotation) -> bool:
     return any(abs(rotation_degrees - angle) < 0.1 for angle in [0, 90, 180, 270])
 
 
+def _get_char_fill_key(char):
+    """生成字符回填判定 key，优先使用 pdftext 提供的页内 char_idx。"""
+    char_idx = char.get('char_idx')
+    if char_idx is not None:
+        return ('char_idx', char_idx)
+    return ('object_id', id(char))
+
+
+def _iter_line_chars(line):
+    """按 pdftext line/span 结构展开字符，兼容缺少 chars 字段的异常 span。"""
+    for span in line.get('spans', []):
+        for char in span.get('chars', []):
+            yield char
+
+
+def _is_visible_standard_rotation_char(char) -> bool:
+    """判断字符是否是可见的标准方向正文字符，避免换行控制符误放行水印。"""
+    text = char.get('char', '')
+    if not text or text.isspace() or text in {'\r', '\n'}:
+        return False
+
+    bbox = char.get('bbox')
+    if not bbox:
+        return False
+
+    x0, y0, x1, y1 = [float(v) for v in bbox]
+    return (
+        x1 > x0
+        and y1 > y0
+        and _is_supported_rotation(char.get('rotation', 0))
+    )
+
+
+def _get_chars_for_span_fill(page_chars):
+    """选择允许参与 span 回填的字符，保留正文内仿斜体并过滤整行斜向水印。"""
+    all_chars = page_chars['chars']
+    fill_char_keys = {
+        _get_char_fill_key(char)
+        for char in all_chars
+        if _is_supported_rotation(char.get('rotation', 0))
+    }
+
+    rotated_chars = [
+        char for char in all_chars
+        if not _is_supported_rotation(char.get('rotation', 0))
+    ]
+    if not rotated_chars:
+        return [
+            char for char in all_chars
+            if _get_char_fill_key(char) in fill_char_keys
+        ]
+
+    for line in get_lines_from_chars(all_chars):
+        if not _is_supported_rotation(line.get('rotation', 0)):
+            continue
+
+        line_chars = list(_iter_line_chars(line))
+        if not any(_is_visible_standard_rotation_char(char) for char in line_chars):
+            continue
+
+        # 标准方向正文行内的局部旋转字符通常是仿斜体强调，需要允许回填。
+        for char in line_chars:
+            if not _is_supported_rotation(char.get('rotation', 0)):
+                fill_char_keys.add(_get_char_fill_key(char))
+
+    return [
+        char for char in all_chars
+        if _get_char_fill_key(char) in fill_char_keys
+    ]
+
+
 def _prepare_post_ocr_spans(need_ocr_spans, spans, pil_img, scale):
     if len(need_ocr_spans) == 0:
         return spans