The invention relates to an asymmetric multidentate azacyclic metal complex and a preparation method thereof. The preparation method comprises the following steps: (1) under the protection of nitrogen, adding diethyl ether and aniline into a reactor, adding butyl lithium the mole of which is equal to to that of the aniline into the reactor at -5-5DEG C, reacting the components overnight at the normal temperature, adding trimethylsilyl chloride into the reactor, reacting the above components for 12 hour; filtering the reaction solution, adding butyl lithium the mole of which is equal to that of the aniline into the filter solution, reacting the mixture for 12 hour; filtering the reaction solution and carrying out vacuum drying; (2) under the protection of nitrogen, adding n-hexane, adding the dimethylamino nitrile or 1-piperidine nitrile the mole of which is two times as much as that of the aniline at -5-5DEG C, reacting the components for 10 hour, adding the zirconium tetrachloride or hafnium tetrachloride the mole of which is 0.5 times as much as that of the aniline at -5-5DEG C, heating the system to the room temperature, reacting the mixture for 5-20 hour, filtering the reaction solution, and concentrating the filter solution, so as to obtain the asymmetric multidentate azacyclic metal complex. In the presence of cocatalyst methylaluminoxane, the complex has good ethylene catalytic activity.