The invention relates to a preparation method of a gadoleic acid bromine lactonized product. A structural formula of the gadoleic acid bromine lactonized product is shown as follows: the formula is shown in the description. The method comprises the following steps: dropwise adding a dichloromethane solution of diphenylsulfoxide (1.5eq) into a dichloromethane solution of oxalyl bromide (1.5eq) at -78 DEG C; then dropwise adding a raw material gadoleic acid; cooling to 0 DEG C and reacting to obtain a corresponding bromine lactonized product. If the gadoleic acid is 3-gadoleic acid and 4-gadoleic acid, a gamma-lactone product is obtained; if the gadoleic acid is 5-gadoleic acid, a delta-lactone product is obtained; the yield is 50 percent to 95 percent.