Abstract: The experimental research on velocity distribution in multiple parallel narrow channels formed by fuel plane of assembly is carried out under various Re and the water without ions as fluid in testing loop. The experimental results show that under various Re within a channel the velocity in the middle area is high and the velocity in the edge of channel decreases rapidly to zero, and the velocity is symmetrically distributed along the centra line, thus the velocity distribution within a channel is like a trapezium. While in parallel channels the velocity of the middle channel is low and the velocity of the channel close to the edge is high, it is supposed to be caused by the inlet structure of channels,this concave distribution is a disadvantage to the even distribution of reactor flux.