Abstract: The accurate mass and metastable ion detections of symmetrical molecule 2,6—(bisdimethylaminomethyl)—4—ethyl phenol dihydrochloride demonstrated. (1) the respective fragments m/z 176, 191, 192, 193, 161 are formed from molecular ion M~+ on the fragmentation mechanism via various cleavage modes; (2)the base peak at m/z 191 is formed with the loss of a neutral molecule via the ortho effect; (3) the base peak m/z 191 may further be cleaved to form fragments m/z 147, 132, 91; (4) the cleavage of C--N bond in side chain of amine group attached to benzene ring is simillar to the symmetrical molecules and on the contrary, dissimilar to the asymmetrical molecules in which the C--N bond is stable and does not cleave.On the basis of fragmentation mechanism~(1.2), comparison between the ortho effects of asymmetrical and symmetrical molecules showed obvious distinctions of them.