The effects of helium plasma seed treatment on lettuce growth under salt stress were studied. Lettuce seeds were treated with an atmospheric dielectric barrier discharge (DBD) helium plasma at different discharge voltages and then planted in different concentrations of salt solution hydroponic tanks. The results show that under the same NaCl concentration (6 g/L), with the increase of the treatment voltage, the growth and quality of the lettuces gradually improved, as confirmed by the measurement of seedling height, root length, the contents of chlorophyll and nitrogen in the leaves. Similarly, under the same treatment voltage (45 kV), with an increase in NaCl concentration, the promotion effect of plasma treatment gradually strengthens, as verified through significance analysis. These results indicate that plasma seed treatment could improve the salt resistance of lettuces.