1:首先下载log4net.dll，通过网上直接download 或者nuget 下载dll都可以。然后把下载下来的Nlog.dll ,Nlog,extension.dll 加入项目reference.
2:配置WebConfig文件：
<configuration>
<configSections>
<section name="nlog" type="NLog.Config.ConfigSectionHandler, NLog"/>
</configSections>
<log4net >
???<!--定义输出到文件中-->
???<appender name="logf" type="log4net.Appender.RollingFileAppender">
?????<!--定义文件存放位置-->
?????<file value="D:\YouPinLog\webinfo\" />
?????<appendToFile value="true" />
?????<param name="DatePattern" value="yyyyMMdd".txt"" />
?????<rollingStyle value="Date" />
?????<maxSizeRollBackups value="100" />
?????<maximumFileSize value="1024KB" />
?????<staticLogFileName value="false" />
?????<Encoding value="UTF-8" />
?????<filter type="log4net.Filter.LevelRangeFilter">
???????<param name="LevelMin" value="INFO" />
???????<param name="LevelMax" value="INFO" />
?????</filter>
?????
?????<layout type="log4net.Layout.PatternLayout">
???????<!--输出格式-->
???????<!--样例：2008-03-26 13:42:32,111 [10] INFO ?Log4NetDemo.MainClass [(null)] - info-->
???????<conversionPattern value="%date %-5level %logger ?- %message%newline" />
?????</layout>
???</appender>
???<root>
?????<appender-ref ref="logf" />
???</root>
???<logger name="DALLogger" additivity="false">
?????<!--additivity 是否确认子日志对象继承父日志对象的appender列表，默认为True:确认-->
?????<!--注意优先级，优先级低的要放在后面-->
?????<level value="ALL" />
?????<appender-ref ref="logf" />
???</logger>
?</log4net>
</configuration>
3：写入日志：
private static readonly ILog loggerDal = LogManager.GetLogger("DALLogger");
loggerDal.Info("info 日志");
loggerDal.Error("Trace 日志");
log4net日志使用方法
原文地址：http://www.cnblogs.com/xiaojw/p/7891519.html