Optical time domain reflectometer(OTDR) on-line detection at the transmitter will affect the service signal, so it is rarely used in practical engineering. In order to explore the specific impact of OTDR at the transmitter on the service signal light, the relationship between the dynamic range of OTDR and the power of optical pulse has been analyzed theoretically. The influence of on-line detection of OTDR at the transmitter on traffic signal light and its reasons are studied experimentally based on 200 Gb/s and 2 Mb/s transmission system. The experimental result shows that the influence of the OTDR on-line detection on the communication service is related to the incident optical power, the dynamic range of the OTDR and the system margin. The strong optical pulse which is generated by OTDR at the transmitter will cause the fluctuation of intensity and the time-domain pulse, which will affect the communication service.