Abstract: Extracted essential oils,flavonoids,and pectin from pomelo leaves,peel,grapefruit meat and seeds using the method of steam distillation,ultrasonic assisted solvent extraction and acid extraction and alcohol precipitation was studied. Essential oils was analyzed by using the method of gas chromatography- mass spectrometry( GC-MS). Besides,the determination of total flavonoids and pectin used the method of Na NO2- Al( NO3)3and carbazole- sulfuric acid. Finally the antioxidant activity of essential oils,flavonoids and pectin was evaluated by using the method of reducing power and scavenging the capability of 1,1- diphenyl-2- picrylhydrazyl( DPPH·).And the antimicrobial activity was evaluated by using the method of filter paper diffusion.The results showed that,the contents of essential oils and flavonoids were the highest in the pomelo peel.And the contents of pectin were the highest in the pomelo meat.There were 25 kinds of compounds detected in pomelo peel oil,mainly D- limonene( 77.96%),beta myrcene( 12.40%) and beta pinene( 2.14%). Pomelo three active ingredients( essential oils,flavonoids and pectin) had strong reducing power,and the IC50 of DPPH·( the concentration of clearance rate were reached to 50%) were 1.53%,0.07% and 0.21%,respectively. Those all showed the strong antioxidant activity.There was different effect on the antibacterial of the three bacteria( Escherichia coli,Staphylococcus aureus and Salmonellai).And with the increasing of mass concentration,the bacteriostatic effects of bacteria were gradually increased.