In general, the data obtained from direct performance test of centrifugal fan is the most intuitive and accurate. But it is also the most complex, but in order to get accurate data results, even if it is complex, it is the first verification method for many users. Drill a hole at the inlet and outlet pipes of the centrifugal fan to measure the static pressure at the inlet and outlet of the centrifugal fan. According to the static pressure of the centrifugal fan, the operation efficiency of the fan is estimated. This method is simple and does not affect the production, but requires professional knowledge of the centrifugal fan. For the high-speed centrifugal fan with inlet regulating damper, if the opening of regulating damper is less than 95%, the centrifugal fan must be in low efficiency operation state. If the regulating damper cannot be fully opened, it will cause two effects. One is that the inlet air flow of the centrifugal fan is uneven, which reduces the aerodynamic performance of the centrifugal fan. Second, there will be pressure loss. According to the calculation of centrifugal fan with flow rate of 10W cubic meters per hour, the motor power of 4kw is required for every 100Pa pressure loss.