  Liquid Argon (LAr) is used as a target material in several current and
planned experiments related to dark matter direct searching and neutrino
detection. Argon provides excellent Pulse Shape Discrimination (PSD) capability
which could separate the electron recoil backgrounds from the expected nuclear
recoil signals. This essay simulated the PSD capability of an LAr detector when
PMTs or three kinds of SiPMs are used as photosensors based on the experimental
data. The results show that the J-60035 SiPM could help the LAr detector
achieve the highest PSD capability event though SiPM's After-Pulse (AP) and
Cross-Talk (CT) deteriorate its PSD capability. In addition, the results also
show that the effect from AP is greater than CT. This is instructive for
selecting photosensors for LAr detectors.
