The invention provides an expression vector containing a recombined blue algae antiviral protein N nucleotide sequence, a host cell containing the expression vector and a method for preparing recombined blue algae antiviral protein on the basis to obtain the recombined blue algae antiviral protein and further proves that the expression vector and/or the host cell and/or the recombined blue algae antiviral protein can be applied to prepare an antiviral medicament. The method of the invention overcomes the disadvantages of low yield, an easily formed inclusion body and difficult purification and the like in the prior art. Peptide mass fingerprinting of the recombined CVN protein prepared by the method is totally consistent with theoretical peptide mass fingerprinting; and an antiviral experiment proves that the recombined protein has good antiviral activity.