Coagulant is coated on the inner wall of the blood-collecting tube, accelerating blood coagulation and minimizing testing duration. Tube contains separation gel, which completely separates blood liquid component (serum) from solid component (blood cells) and aggregates both components inside the tube with barrier. Product can be used for blood biochemistry tests (liver function, renal function, myocardial enzyme function, amylase function, etc), serum electrolyte tests (serum potassium, sodium, chloride, calcium, phosphate, etc), thyroid function, AIDS, tumor markers, serum immunology, drug testing, etc.