Provided are an improved lentiviral expression vector, a construction method for same, and applications thereof. The plasmid backbone of the lentiviral expression vector is based on pLVX-Puro and is improved via the following steps: a. adding a CMV enhancer and promoter to the upstream of 5′ LTR by means of gene synthesis and subcloning; b. replacing the original 5′ LTR with a new 5′ LTR (SEQ ID NO: 3) of which the length is 181 bps; c. replacing the CMV promoter on an original vector with an EFS promoter; d. deleting a PGK promoter after multiple cloning sites of the original vector and, at the same time, introducing a P2A connection subsequence; e. replacing original resistance against Puro with resistance against a shorter Blasticidin; and f. replacing original 3′ LTR with an LTR (SEQ ID NO: 7) with a partially deleted U3. The lentiviral expression vector acquired by the improvement provides a greater packaging capacity in comparison with pLVX-Puro.