App.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section name="log4net"  type="log4net.Config.Log4NetConfigurationSectionHandler,log4net"/>
  </configSections>
  <log4net>
    <root>
      <level value="debug" />
      <appender-ref ref="LogFileAppender" />
    </root>
    
    <logger name="KangarooLog">
    </logger>
    
    <appender name="LogFileAppender" type="log4net.Appender.FileAppender">
     
      <file value="D:/log4netfile.txt" />
      <appendToFile value="true" />

      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="记录时间：%date 线程ID:[%thread] 日志级别：%-5level 出错类：[%class] - 错误描述：%message%newline" />
      </layout>
    </appender>

  </log4net>
</configuration>

static void Main(string[] args)
        {
            ILog log = LogManager.GetLogger("KangarooLog");
            log.Debug("ffffffffffffffffff");
            Console.Read();
        }

[assembly: log4net.Config.XmlConfigurator(ConfigFile = "App.config", Watch = true )]