We investigate the infall properties in a sample of 11 infrared dark clouds (IRDCs) showing blue-asymmetry signatures in HCO+ J=1-0 line profiles.We used JCMT to conduct mapping observations in HCO+J=4-3 as well as single-point observations in HCO+J=3-2,towards 23 clumps in these IRDCs.We applied the HILL model to fit these observations and derived infall velocities in the range of 0.5-2.7km s-1,with a median value of 1.0km s-1,and obtained mass accretion rates of 0.5-14 × 10-aM☉ yr-1.These values are comparable to those found in massive star forming clumps in later evolutionary stages.These IRDC clumps are more likely to form star clusters.HCO+J=3-2 and HCO+J=1-0 were shown to trace infall signatures well in these IRDCs with comparable inferred properties.HCO+ J=4-3,on the other hand,exhibits infall signatures only in a few very massive clumps,due to smaller opacities.No obvious correlation for these clumps was found between infall velocity and the NH3/CCS ratio.