The present invention provides a kind of polymer that cytotoxicity is low, preparation method and medical instrument surface treating agent, which can give surface hydrophilicity and biocompatibility to surfaces such as medical instruments by easy processing. Polymer of the invention is the polymer of specific weight average molecular weight, the polymer have special ratios formula (1a) and (1b) shown in structural unit, and may be used as the surface treating agent of various medical instruments. X:本發明提供一種細胞毒性低的聚合物、其製備方法以及醫療器械用表面處理劑，該聚合物通過簡便的處理可對醫療器械等表面給予表面親水性和生物相容性。本發明的聚合物是特定的重量平均分子量的聚合物，該聚合物具有特定比例的式(1a)及(1b)所示的結構單元，並可以用作各種醫療器械的表面處理劑。X：
