The invention provides a boron-assistant crown ether compound and its preparation method and use. The boron-assistant crown ether compound has a structure shown in a general structural formula 1 and in the formula, groups are defined in the specification. Boron is introduced into crown ether, the boron-assistant crown ether with electric neutrality and an alkali metal complex can improve extraction distribution and separation coefficients, the boron-oxygen bond-closed boron-assistant crown ether compound as an extraction agent can be subjected to proton ring opening and realizes selective alkali metal ion complexing opening and closing, and the boron-assistant crown ether compound solves the problem of alkali metal ion extraction and separation based on the traditional crown ether and has a wide application prospect in alkali metal ion extraction and separation and especially in lithium ion separation.