Abstract: The objective was to explore salt tolerance gene NHX expression pattern in three kinds of fiber flax using semi-quantitative RT-PCR technology stressed with NaCl. Total RNAs were extracted respectively from the sterile stem-leaf tissues stressed with different concentration of NaCl for 6 d. cDNA were reversely transcribed. Expression quantities of NHX gene in the different groups were detected by optimized semi-quantitative RT-PCR method. The results showed that the highest expression quantities of NHX gene in‘Fanny’and‘Shuangya 5’sterile seedlings stressed with 100 mmol/L NaCl for 6 d and in‘Tianxin 3’sterile seedlings stressed with 200 mmol/L NaCl for 6 d. Expression quantities of NHX gene in the three kinds of fiber flax after salt stresses were all up regulation compared with contrasts. Therefore, detection of NHX gene could be used as an index judging salt tolerance of these three kinds of fiber flax.