The invention relates to an efficient composite heavy metal chelating agent and a preparation method thereof. The efficient composite heavy metal chelating agent comprises the components in percentage by mass as follows: 35%-40% of nanometer aluminum oxide, 15%-20% of ethylene diamine tetraacetic acid and 40%-60% of sodium carboxymethyl starch. The efficient composite heavy metal chelating agent is non-toxic and has no harm to aquatic lives, pH value is not required to be adjusted when heavy metal wastewater is treated, and the treatment effect is superior to that of a traditional heavy metal treatment method.