A novel method aiming at analyzing the effect of dedicated bus lanes (DBLs) in improving bus operation performance based on secondary speed difference concept was proposed. With global positioning system (GPS) data of buses and cabs, stop data and road segment data from 54 roads in Shenzhen City, we analyzed the speed characteristics of DBLs on major urban roads in Shenzhen City, characterized the quantified effect of DBLs using the secondary speed difference of bus and cab with the bias of vehicle travelling difference and bus stop eliminated, and verified the significance level of this effect. The results show that DBL brings a remarkable effect on secondary speed difference while factors including bus stop density, bus stop form and bus stop location do not; DBL is effective in improving bus operation performance, the using of DBL will significantly reduce the speed difference between bus and other vehicles, thereafter improves operation efficiency, however some of DBLs are not effective.