Abstract: Based on numerical simulation,the flow distributions of the ordinary header and three improved headers was studied with PIV, and a series of velocity streamline graphs of different cross sections were obtained.At Re＝6.22×10⁴ the outlet flow distributions of the ordinary header and an improved header, and the effects of flow distribution of three improved headers with different middle-hole-area ratios were compared.The experimental results showed that the perforated plate header configuration could effectively improve the uniformity of fluid flow distribution.Flow maldistribution parameter S_U and the ratio of the maximum velocity to the minimum velocity θ_U of the type C header configuration were minimum.There was an optimum point between flow distribution and the middle-hole-area ratio.