Triggering mechanisms of solar eruptions have long been a challenge .
A few previous case studies have indicated that preceding gentle filament merging via magnetic reconnection may launch following intense eruption , according with the tether-cutting ( TC ) model .
However , detailed process of TC reconnection between filaments has not been exhibited yet .
In this work , we report the high resolution observations from the Interface Region Imaging Spectrometer ( IRIS ) of TC reconnection between two sheared filaments in NOAA active region 12146 .
The TC reconnection commenced since \sim 15:35 UT on 2014 August 29 and triggered an eruptive GOES C4.3-class flare \sim 8 minutes later .
An associated coronal mass ejection appeared in the field of view of SOHO /LASCO C2 about 40 minutes later .
Thanks to the high spatial resolution of IRIS data , bright plasma outflows generated by the TC reconnection are clearly observed , which moved along the subarcsecond fine-scale flux tube structures in the erupting filament .
Based on the imaging and spectral observations , the mean plane-of-sky and line-of-sight velocities of the TC reconnection outflows are separately measured to be \sim 79 and 86 km s ^ { -1 } , which derives an average real speed of \sim 120 km s ^ { -1 } .
In addition , it is found that spectral features , such as peak intensities , Doppler shifts , and line widths in the TC reconnection region evidently enhanced compared with those in the nearby region just before the flare .