1.查看日志文件名 使用命令 
sp_helpdb testdb
2.
USE [master]
GO
ALTER DATABASE testdb SET RECOVERY SIMPLE WITH NO_WAIT
GO
ALTER DATABASE testdb SET RECOVERY SIMPLE
GO
USE testdb 
GO
DBCC SHRINKFILE (N'Csoft_log' , 0,TRUNCATEONLY)
GO
USE [master]
GO
ALTER DATABASE testdb SET RECOVERY FULL WITH NO_WAIT
GO
ALTER DATABASE testdb SET RECOVERY FULL
GO

注：适用sql 2005及以上版本