Abstract: The noise analyses in the reconstruted heavy water research reactor(HWRR-3) and the loop of high temperature and pressure are described. Thesignals of neutron, temperature, flow and pressure are recorded by multichannelanalog magnetic recorder and are analysed by the dynamical signal analyser ofSD375 type, to obtain auto-power spectrum density (APSD), cross-power spectrumdensity, phase shift, coherence and transfer function. In the normal condition,there are two dominant peaks on the APSD at 2.3Hz and 6.8Hz respectivly. Inthe anomalous condition, there is another dominant peak on the APSD at 0.7Hz.In the fault condition, the dominant peak at 0.7Hz split apart into two peaksoverlaped each other on the APSD at 0.5Hz and 0.9Hz.