The invention provides application of a nucleic acid construct containing streptavidin elements to protein expression and purification, and particularly provides the nucleic acid construct. The nucleic acid construct has a formula I structure from 5' to 3', and the formula I is as follows: Z1-Z2-Z3 (I); and in the formula I, Z1, Z2 and Z3 are the elements used for constituting the construct correspondingly, all '-' are bonds or nucleotide connection sequences independently, Z1 represents a coding sequence of a tag protein, Z2 represents a connection sequence, and Z3 represents a coding sequence of a passive protein or a foreign protein. By applying the nucleic acid construct to a protein synthesis system (especially an in-vitro protein synthesis system), expression and purification of theforeign protein can be completed, and an RFU value of the synthesized foreign protein is increased.