The invention discloses a computer case dust-prevention device. The computer case dust-prevention device comprises a case shell, a dust-prevention net cover, a dust containing box and a built-in windshield, wherein case mounting side plates are mounted above the case shell; a fan net cover is arranged above the dust-prevention net cover; a containing box mounting groove is formed above a small exhaust fan; the upper part of the containing box mounting groove is connected with the dust containing box; a gas delivering tube is mounted below the dust containing box; a flow speed controller is mounted below the gas delivering tube; the lower part of the flow speed controller communicates with a gas inlet; the built-in wind shield is mounted in the dust containing box; a dust flowing-out opening is formed in the lower part of the built-in wind shield; a solenoid control valve is mounted below the dust flow-out opening; and a side plate mounting groove is formed in the upper part of each case mounting side plate. The computer case dust-prevention device has the beneficial effects that dust in a computer case can be prevented effectively, it can be ensured that a computer runs normally,and the use effect is good.