Pretreatment of TiNi alloy by implantation of phosphorus can be used to make beta-particle-emitting radioactive stents. The compositions, phase constitutions and hemocompatibility of a P-ion-implanted (PII) TiNi alloy are studied by means of XPS, DSC and the plates adhesion tests. It is shown that a 40 nm thick P-rich layer is formed on the surface of PII treated TiNi alloy. This layer mainly consists of P, O, Ti and a little Ni. The valence band electron density of the PII treated alloy is lower than that of untreated alloy. The P-rich layer consists of three phases, phosphide, martensite and parent phase. DSC curves of the PII treated TiNi alloy show a broader endothermal and exothermal peaks, and martensitic transformation temperature (Ms) of TiNi alloy increases by PII treatment. Moreover, during heating the reverse transformation process of the untreated TiNi alloy is as following: M-->R-->A, but the PII alloy gives no evidence of the R phase transformation. Comparing to the untreated TiNi alloy, the platelets adhered to the PII alloy surface is fewer and the paltelets have less deformation. The hemocompatibility of TiNi alloy may be improved by PII treatment.