The invention provides a reagent, preparation method and application for separating and extracting plasma protein and nucleoprotein in cells. The reagent includes lysate A: 6mM-12mM HEPES with a pH of 7.8, 9mM-11mM NaCl, 0.5 mM EDTA, 1mM- 2mM MgCl 2 ; Lysis Buffer B: 6mM‑12mM HEPES pH 7.8, pH 7.8, 9mM‑11mM NaCl, 0.5 mM EDTA, 1mM‑2mM MgCl 2 , 8%‑12% NP‑40; Lysis Solution C: 6mM‑12mM HEPES, pH 7.8, 9mM‑11mM NaCl, 0.5 mM EDTA, 1mM‑2mM MgCl 2 , 8%-12% glycerin, 8%-12% SDS. The invention can realize efficient, rapid and complete separation of cytoplasmic protein and nucleoprotein, and avoid cross contamination of the two.