Abstract: A method has been developed for the determination of trace cobalt and nickel in heavy water and precipitates in reactor active region, as well as in several kinds of reactor loop washing liquids. The objective of this work is to analyse the samples collected during the period of the reconstruction of the HWRR which has served for 20 years.1. Optitum conditions are found after testing the influences of several solutions on the determination of Co, Ni by catalytic polarography. Base solution consists of 0.5 M NH4OH,0.7M NH4C1O4 and 0.01 M Na2C3H4O6 (sodium tartrate) and 0.04% dimethylglyoxime (alcohol solution).2. Impurities such as Zr, Ru, Cs, Cr, etc. do not interfere with the catalytic wave of Co, Ni.3. Components in washing liquids used for decontamination such as H3PO4, HNO3, KMnO4, H2C2O4, NH4H2cit (ammonium dihydric citrate) are tested to ascertain^ their effects on the catalytic wave of Co, Ni, and a working curve is constructed for the analysis of the actual samples.4. This method is proved to be sensitive, simple, rapid and inexpensive. Besides, it has the adventage of easy shielding against radioactivity. It is also superior to general polarography or spectrophotometric method. The detection limits of the method for Co is 5-250 ppb, for Ni 7-380 ppb.5. This method has been applied to the determination of samples which consist of 11 species of different constituents and radioactivities with satisfactory results. From the analytical results it can be seen that the impurities come from reactor washing and decontamination, corrosion and erosion of metal, depth of corrosion and the spread of radioactivity of 60Co. The results of the determination provide an important basis for assessing whether the reactor loop can be continually operated with safety.