The standard kε-turbulence model and the two phase flow Eulerian model are used to simulate the refrigerant distributions in the heads of parallel-flow evaporators, and the experimental results in literature is used to validate the numerical method. Then, the comparison of distributions between base line structure and the structure with perforated tube in heads is conducted and the reason behind the performance improvement of the structure with perforated tube is revealed. The comparison of flow distribution in heads with perforated tubes in the open ratio ranging from 0.11 to 1.00 indicates that the uniformity of flow distribution decreases at first and then increases, after which it worsens with the further increase of open ratio. The matching issue of expansion valve with refrigerant systems should be concerned under the condition of small open ratio of perforated tubes.