  Several mechanisms for the transformation of blue star-forming to red
quiescent galaxies have been proposed, and the green valley (GV) galaxies amid
them are widely accepted in a transitional phase. Thus, comparing the
morphological and environmental differences of the GV galaxies with early-type
disks (ETDs; bulge dominated and having a disk) and late-type disks (LTDs; disk
dominated) is suitable for distinguishing the corresponding quenching
mechanisms. A large population of massive ($M_* \geqslant 10^{10}M_\odot$) GV
galaxies at $0.5 \leqslant z \leqslant 1.5$ in 3D-HST/CANDELS is selected using
extinction-corrected $(U-V)_{\rm rest}$ color. After eliminating any possible
active galactic nucleus candidates and considering the "mass-matching", we
finally construct two comparable samples of GV galaxies with either 319 ETD or
319 LTD galaxies. Compared to the LTD galaxies, it is found that the ETD
galaxies possess higher concentration index and lower specific star formation
rate, whereas the environments surrounding them are not different. This may
suggest that the morphological quenching may dominate the star formation
activity of massive GV galaxies rather than the environmental quenching. To
quantify the correlation between the galaxy morphology and the star formation
activity, we define a dimensionless morphology quenching efficiency $Q_{\rm
mor}$ and find that $Q_{\rm mor}$ is not sensitive to the stellar mass and
redshift. When the difference between the average star formation rate of ETD
and LTD galaxies is about 0.7 $M_\odot \rm \;yr^{-1}$, the probability of
$Q_{\rm mor}\gtrsim 0.2$ is higher than 90\%, which implies that the degree of
morphological quenching in GV galaxies might be described by $Q_{\rm
mor}\gtrsim 0.2$.
