In order to reveal the indicating significance of magnetic susceptibility of river floodplain sediments, the magnetic susceptibility has been determined by using 3 river floodplain sediment cores of 100 cm at the lower reaches of the Yangtze River between Zhenjiang and Yangzhou. It can be found that: the magnetic susceptibility of old river floodplain sediment core SY7 ranges from 12. 11×10^-8 m³/kg to 30. 60×10^-8 m³/kg, for the average in 20. 79×10^-8 m³/kg; the magnetic susceptibilities of SY5 and Z2 in the modern river floodplain sediments are obviously larger, the highest average value of SY5 is 123. 20×10^-8 m³/kg, and the modern river floodplain’s magnetic susceptibility is 5-6 times of old river floodplain sediments. Heavy metal pollution in the river floodplain sediments of the study area was compared with the background values of stream sediments in the Yangtze River basin, and the heavy metal pollution in Cu, Ni and Cr was more serious. Meanwhile, the pollution of newly formed river floodplain was more severe than that of old river floodplain. Simple and rapid determination of magnetic susceptibility can be used as one of important means for diagnosing heavy metal pollution in floodplain sediments.