Abstract: Through the investigation and measurement of underground ventilation system in Caolou Iron Mine，it is found that there are some problems such as short circuit of air flow in the middle section of -170 m and -230 m，excessive wind resistance in some operation sites in the middle section of -290 m， and low supply and demand ratio of air flow in the middle section of -350 m and -410 m. Therefore，by adding auxiliary fans to solve the problem of excessive local wind resistance，the measures of zoning venti⁃ lation，replacing adjusting air doors and constructing ventilation roadways are taken to improve the supply and demand ratio of air volume，and the operation frequency of existing fans is adjusted according to the ventilation demand during the production period. Through on-site testing，the measures have achieved the expected requirements after implementation.

Key words: ventilation system, wind resistance, air doors