Particulate matters, being one of the major indoor contaminates, can lead to serious effect to our health, especially for those having the aerosol diameter less than lOum (PM10), since those are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects. Therefore, concern should be paid to the indoor pollution from PM10. In this study, the particulate matters of an industrial workshop are suspected to be at a high concentration, therefore, an investigation has been performed to check the level of the particulate matters and the air flow path of them. The investigation is conducted by two means: experimental measurement for the particulate matter and computational simulation for the air flow field of the room. Experimental data showed that the particulate matters are much higher than the Hong Kong indoor air quality objective value which is 0.180mg/m3 [1] and simulation results showed that the particulates generated are spreading everywhere within the room before extracted away by the HVAC system. In order to protect the occupants inside the room, the HVAC system is proposed to be modified into a three-level negative pressure system. Performance of the three-level negative pressure system is verified by CFD tool and result showed that the new HVAC system can immediately extracted the contaminants away without contaminating the occupants inside.