To understand the nature of SiO emission, we conducted ACA observations of the SiO (2-1) lines toward 146 massive starforming regions, as part of the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey. We
detected SiO emission in 128 (87.7 per cent) sources and identified 171 SiO clumps, 105 of which are spatially separated from
3 mm continuum emission. A large amount of the SiO line profiles (60 per cent) are non-Gaussian. The velocity dispersion of the
SiO lines ranges from 0.3 to 5.43 km s−1. In 63 sources the SiO clumps are associated with HII regions characterized by H40α
emission. We find that 68 per cent (116) of the SiO clumps are associated with strong outflows. The median velocity dispersion
of the SiO line for outflow sources and non-outflow sources is 1.91 km s−1 and 0.99 km s−1, respectively. These results indicate
that outflow activities could be connected to strongly shocked gas. The velocity dispersion and [SiO]/[H13CO+] intensity ratio
do not show any correlation with the dust temperature and particle number density of clumps. We find a positive correlation
between the SiO line luminosity and the bolometric luminosity, implying stronger shock activities are associated with more
luminous protoclusters. The SiO clumps in associations with HII regions were found to show a steeper feature in Lsio/Lbol.
The SiO line luminosity and the fraction of shocked gas have no apparent evidence of correlation with the evolutionary stages
traced by luminosity to mass ratio (Lbol/M).