被我找到了，最近也在看Typecho
修改文件var/Widget/Register.php 第 68 行：

$dataStruct = array(
    'name'      =>  $this->request->name,
    'mail'      =>  $this->request->mail,
    'screenName'=>  $this->request->name,
    'password'  =>  $hasher->HashPassword($generatedPassword),
    'created'   =>  $this->options->gmtTime,
    'group'     =>  'subscriber'
);