The invention relates to a new method for improving the drought resistance of brassica napus. Before sowing, dielectric barrier helium low temperature plasma treatment is conducted on brassica napus seeds, and the treatment conditions include: power 300-450 W, time 30-90 s, pressure intensity 50-150 Pa and pole plate spacing 2 cm; foliage spraying is conducted on drought-stressed brassica napus seedlings, a drought-resisting agent is irrigated to roots, and the drought-resistant agent component comprises 5-aminolevulinic acid 50-100 mg / L, hydrogen-rich water (hydrogen concentration of 0.05-0.2mmol / L), boric acid 1-3 g / L and tween-80 0.1%-0.3%. The method can significantly improve the drought resistance of the brassica napus. Under drought stress, by adopting the method, the stem diametersof the seedlings are increased by 14%-22%, leaf thickness is increased by 16%-22%, the dry weight of overground parts is increased by 14%-28%, the dry weight of underground parts is increased by 14%-24%, the root activity is increased by 17%-21%, the net photosynthetic rate is increased by 17%-24%, the N content of leaves is increased by 17%-22%, and the SOD activity of the leaves is increased by16%-36%. The method is low in cost, simple and easy to operate, safe and environmentally friendly, and can alleviate the damage caused by drought stress on the brassica napus seedlings and significantly improve the drought resistance of the brassica napus seedlings.