App.config里面配置:

<?xml version="1.0"?>
<configuration>


  <configSections>
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net"/>
  </configSections>
  <log4net>
    <appender name="FileAppender" type="log4net.Appender.FileAppender">
      <file value="log\\mylog.log"></file>
      <appendToFile value="true"></appendToFile>
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="[%d]:%n%m%n"></conversionPattern>
      </layout>
    </appender>
    <appender name="ConsoleAppender" type="log4net.Appender.ConsoleAppender">
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="[%d]:%n%m%n"></conversionPattern>
      </layout>
    </appender>
    <root>
      <level value="INFO"></level>
      <appender-ref ref="FileAppender"></appender-ref>
      <appender-ref ref="ConsoleAppender"></appender-ref>
    </root>
    <logger name="MyLogger">
      <level value="ERROR"></level>
      <appender-ref ref="FileAppender"></appender-ref>
      <appender-ref ref="ConsoleAppender"></appender-ref>
    </logger>
    </log4net>


    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
    </startup>
</configuration>

AssemblyInfo.cs里面配置:

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

Program.cs里面

log4net.Config.XmlConfigurator.Configure();