diff --git a/woa/init.py b/woa/init.py
index 9d52495..be5516f 100644
--- a/woa/init.py
+++ b/woa/init.py
@@ -37,7 +37,9 @@ class WOAHandler:
 		self.aes_key = None
 		if encoding_aes_key:
 			# 微信的 AES Key 是 base64 编码的 32 字节字符串
-			self.aes_key = base64.b64decode(encoding_aes_key)
+			def add_padding(s):
+				return s + '=' * (4 - len(s) % 4) if len(s) % 4 != 0 else s
+			self.aes_key = base64.b64decode(add_padding(encoding_aes_key))
 		debug(f'{self.app_id=}::{self.token=}::{encoding_aes_key=}::{len(encoding_aes_key)=}')
 		self.media_manager = WeChatMediaManager(self.app_id, self.secret)