使用QIODevice::WriteOnly | QIODevice::Text试试
m_file.open(QIODevice::WriteOnly | QIODevice::Append);
QString message=QDateTime::currentDateTime().toString("yyyy-mm-dd hh:mm:ss zzz")+" "+textInfo;
QTextStream text_stream(&m_file);
text_stream << message << "\r\n";
m_file.flush();