Abstract: A pool experiment was conducted to study the the effects of combined application of boron(B),molybdenum(Mo),zinc(Zn) on the seed yield and quality of Brassica napus Huashuang 4.The results showed that the treatment of combined application of B,Mo and Zn fertilizers had the highest yield,which increased by 20.7% than the yield of the control treatment(CK).Among the treatments with any two elements(B,Mo and Zn) combined application,BMo treatment had the highest seed yield and no statistically significant difference in yield was founda between the treatments of BMo and BMoZn.In additio,there was no significant difference in yield among the treatments of BZn,MoZn and CK.The number of seed per silique was the highest for the treatment of BMoZn.The siliques per plant and the thousand grain weight were the highest for the treatment of BMo.Combine applying B with other elements could increase the oil content while combine applying Zn with other elements could increase protein content of huashuang 4.The interactions between the microelements used in the present study decreased the glucosindate and erucic acid content of huashuang 4.Combined application of B and Zn decreased the contents of plamic acid(16∶0),lionlenic acid(18∶3) and linoleic acid(18∶2);however,it increased the oleic acid(18∶1) significantly indicating the combined application of B and Zn was in favor of improving component ratio of fatty acid.For double-high rape(high glucosindate and erucic acid content),from the point of increasing seed yield and oil content,BMo was the best treatment.While for double-low rape(low glucosindate and erucic acid content) which cake could be used as animal forge,considering increase in seed yield and the content and quality of oil,with simultaneous increase in protein content of rapeseed cake,BMoZn was the best treatment.