<log4net>
    <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
      <!--日志路径-->
      <param name="File" value="C:App_LogTest" />
      <!--是否是向文件中追加日志-->
      <param name="AppendToFile" value="true" />
      <!--log保留天数-->
      <param name="MaxSizeRollBackups" value="30" />
      <!--日志文件名是否是固定不变的-->
      <param name="StaticLogFileName" value="false" />
      <!--日志文件名格式为:2008-08-31.log-->
      <param name="DatePattern" value="yyyy-MM-dd&quot;.log&quot;" />
      <!--日志根据日期滚动-->
      <param name="RollingStyle" value="Composite" />
      <param name="maxSizeRollBackups" value="10" />
      <param name="maximumFileSize" value="100MB" />
      <layout type="log4net.Layout.PatternLayout">
        <param name="ConversionPattern" value="%d %-5p %c - %m%n" />
      </layout>
    </appender>
    <!-- 控制台前台显示日志 -->
    <appender name="ColoredConsoleAppender" type="log4net.Appender.ColoredConsoleAppender">
      <mapping>
        <level value="ERROR" />
        <foreColor value="Red, HighIntensity" />
      </mapping>
      <mapping>
        <level value="Debug" />
        <foreColor value="Green" />
      </mapping>
      <layout type="log4net.Layout.PatternLayout">
        <header value="[BEGIN LOGGING AT %date]%newline" type="log4net.Util.PatternString" />
        <footer value="[END LOGGING AT %date]%newline%newline" type="log4net.Util.PatternString" />
        <ConversionPattern value="%d [%t] %-5p %c : [行号:%-5L] %m%n" />
      </layout>
      <filter type="log4net.Filter.LevelRangeFilter">
        <param name="LevelMin" value="INFO" />
        <param name="LevelMax" value="Fatal" />
      </filter>
    </appender>
    <root>
      <!--(高) OFF > FATAL > ERROR > WARN > INFO > DEBUG > ALL (低) -->
      <level value="all" />
      <appender-ref ref="ColoredConsoleAppender" />
      <appender-ref ref="RollingLogFileAppender" />
    </root>
  </log4net>

using System;
using log4net;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            log4net.Config.XmlConfigurator.Configure();

            ILog log = LogManager.GetLogger("类名");
            //记录错误日志
            log.Error("This is error", new Exception("发生了一个异常"));
            //记录严重错误
            log.Fatal("This is fatal", new Exception("发生了一个致命错误"));
            //记录一般信息
            log.Info("This is info");
            //记录调试信息
            log.Debug("This is debug");
            //记录警告信息
            log.Warn("This is warn");
            Console.WriteLine("日志记录完毕。");
            Console.Read();
        }
    }
}