The invention discloses an intermediate for synthesizing carbapenems penicillin etapenem having the formula of IV, and a preparation method and application in the preparation of the carbapenems penicillin etapenem thereof. The preparation method comprises the following steps: allowing a compound having the formula of III and activated ester of PNZ L-hydroxyproline to perform condensation reaction in a nonpolar solvent, wherein the PNZ L-hydroxyproline is shown in the formula of IX, PMB is shown in figure (1), and PNZ is shown in figure (2). The intermediate can be used for preparing etapenem side chain, and further etapenem. The preparation method can be carried out at the room temperature, with the advantages of mild reaction condition, low cost, simple operation, simple experiment condition, no requirement of expensive reagent, high yield, environmental friendliness, and easily realized industrial production.