The invention relates to a preparation method of a fused protein of human serum albumin and mutant human granulocyte colony stimulating factor, and the product thereof, belonging to the technical field of long-effetive recombinant fused protein drugs. Human serum albumin(HSA) cDNA and mutant human granulocyte colony stimulating factor(hGCSF) cDNA are directly connected, without adding any connecting peptide therevetween, obtaining HAS- hGCSFm cDNA which is then integrated with a cell of the host to express. The fused protein of the invention comprises a first region with at least 85% of the sequence congenetic with human serum albumin and a second region with at least 85% of the sequence congenetic with the mutant human granulocyte colony stimulating factor, and the two regions are directly connected without any connecting peptide therebetween. Under the premise of not being changed in characteristics, the fused protein is capable of the substitution, deletion or addition of specific amino acid residues. The host cell can be bacteria, barm, insect cell, zooblast, plant cell, etc. The fused protein maintains the physiological characteristics of the mutant human granulocyte colony stimulating factor and prolonges the half life of the mutant human granulocyte colony stimulating factor within human body; therefore the fused protein is of good application prospect in pharmacy.