The optical transmission turbidimetry is used to detect activated partial thromb oplastin time (aPTT),and the surface modification of quartz crystal microbalance (QCM) is studied by using three kind s of materials,which include polyethylene (PE),polystyrene (PS) and Parylene- C.Three kinds of modified QCM (PE-QCM,PS-QCM and P-QCM) were evaluated by network analyzer.In addition,h ydrophobic contact angles are 92.3°,90.7° and 93.3°,respectively.The result s show that the quality of P-QCM device is improved,the effective signal pea k to peak value is increased by 11%,the comparison of optical aPTT detection shows good re peatability,plasma 7times detection coefficient of variation (CV) is 1.51%,and 7w hole blood tests CV is 1.15%.In a conclusion,Parylene-C modified QCM provides key technology of inst rument on domestic aPTT testing.