To understand the nature of SiO emission, we conducted ACA observations of the SiO (2-1) lines toward 146 massive star-forming 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. In 63 sources the SiO clumps are associated with H II regions characterized by H40{alpha} 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 and 0.99 km/s, respectively. These results indicate that outflow activities could be connected to strongly shocked gas. The velocity dispersion and [SiO]/[H^13^CO^+^] 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 H II regions were found to show a steeper feature in L_SiO_ / L_bol_. 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 (L_bol_ / M).