  To meet the timing resolution requirement of up-coming High Luminosity LHC
(HL-LHC), a new detector based on the Low-Gain Avalanche Detector(LGAD),
High-Granularity Timing Detector (HGTD), is under intensive research in ATLAS.
Two types of IHEP-NDL LGADs(BV60 and BV170) for this update is being developed
by Institute of High Energy Physics (IHEP) of Chinese Academic of Sciences
(CAS) cooperated with Novel Device Laboratory (NDL) of Beijing Normal
University and they are now under detailed study. These detectors are tested
with $5GeV$ electron beam at DESY. A SiPM detector is chosen as a reference
detector to get the timing resolution of LGADs. The fluctuation of time
difference between LGAD and SiPM is extracted by fitting with a Gaussian
function. Constant fraction discriminator (CFD) method is used to mitigate the
effect of time walk. The timing resolution of $41 \pm 1 ps$ and $63 \pm 1 ps$
are obtained for BV60 and BV170 respectively.
