To improve the efficiency and reduce the noise of forward multi blade centrifugal fans, performance test and flow field measurement with five hole probe at outlet of impeller were carried out for adjustable casings instead of concealed motor. 为进一步提高风机产品的效率、降低噪声,对内藏电动机式前向多叶离心风机,用3种可伸缩套筒模拟内藏电动机进行了风机性能实验。