From 2011 to 2013, the CHINArray project led by the Institute of Geophysics, China Earthquake Administration, made the first phase deployment of 350 broadband seismometers at the southeastern margin of the Tibetan plateau. The three‐component records of the CHINArray‐I have been widely used in studying seismic structures beneath the margin under the assumption that the two horizontal components of seismometers are well aligned toward geographic north and east. In this study, we estimated the actual orientation of the two horizontal components of the 350 seismometers by analyzing P‐wave particle motions of teleseismic earthquakes. Among the 350 stations, we found 80 stations were mildly misaligned by 5°–20°, and another 49 stations had misorientations larger than 20° or other malfunctioning issues. We also investigated how sensor misalignment affects seismic studies that rely on the vectorial nature of seismic recording, such as constructing receiver functions, estimating seismic anisotropy, and extracting surface wave Green’s functions from ambient‐noise data. We found a large deviation in sensor orientation could result in wrong results or large measurement errors, whereas a mild sensor misalignment tended to decrease measurement stability and reliability.