An inspection of companies based around Beijing found more than 70% were violating air pollution regulations.
Firms pumped out more emissions than allowed, operated without licences or had insufficient pollution control equipment.
Checks were carried out at thousands of companies at 28 cities in and around the Beijing-Tianjin-Hebei region.
The findings appear to confirm suspicions that companies ignore strict environmental protection policies and those officials do not enforce them.
Inspections found that more than 13,000 companies had failed to meet environmental standards, the ministry of environmental protection said in a statement.
The ministry ordered local officials to investigate the firms and rectify the problems, the statement said.
China's government is under pressure to do more to address the sources of smog, including reducing reliance on coal-fired power plants, the country's primary source of electricity.
An inspection of companies based around Beijing found more than 70% were violating air pollution regulations.
