Based on the analysis of current web service applications and protocol, a group of quality of service (QoS) parameters of web traffic is proposed from users' perspective. These parameters focus on delay of web service. A active monitor system is designed and used to monitor web performance on real network of the biggest ISPs in China. These delay parameters are actively measured in this specialized measurement system. Based on measured data, different aspects of user perceived web performance are analyzed in different access methods, target websites and time slots. Some practical valuable conclusions are concluded.