The invention discloses a 1,1,3,3-tetra alkyl guanidine carbonyl cobalt metal organic ion liquid. A structure formula of the ion liquid is shown in the description. The invention also discloses a preparation method of the ion liquid and application of the ion liquid in synthesizing of 3-hydroxy carboxylate by epoxy compound hydroesterification. The 1,1,3,3-tetra alkyl guanidine carbonyl cobalt metal organic ion liquid has the advantages that guanidine cation has the double functions of stabilizing tetra carbonyl cobalt cation and using as a Lewis acid to activate epoxy compound primer; compared with the traditional Co2(CO)8/azacycle catalytic system, the use of a nitrogen-containing organic matter is avoided; the ion liquid can be recycled and repeatedly used, the use rate of carbonyl cobalt is improved, and the production cost is reduced; the stability of the 1,1,3,3-tetra alkyl guanidine carbonyl cobalt metal organic ion liquid is high, the ion liquid can be repeatedly applied to catalysis of epoxy compound hydroesterification for multiple times, the catalytic reaction effect is good, and the separation and recycling are convenient.