Abstract: The paper presents the analysis of power fluctuation in HWRR-3. Autopowerspectrum densities (APSD) of power signals are analysed for various coolantflow at same power and for various power at same coolant flow rate. The experimental results show the following behavior: 1. In the case of lowpower (12kW) and hight flow rate (450m~3h~(-1)), there are two dominant peaks onthe APSD at 0.5Hz and 2.3Hz respectively; 2. In the case of power greater than1000 kW and coolant flow greater than 420m~3h~(-1), there are three dominant peakson the APSD. The frequencys of tow dominant peaks of them at 0.5Hz and 2.3Hz are hardly changed with coolant flow, but for the third dominant peak, thefrequency is changed from 5.5Hz to 6.7Hz with coolant flow rates varied from420m~3h~(-1) to 576m~3h~(-1); 3. The fluctuation of reactor power is significantly depres-sed when flow rate is less than 450m~3h~(-1), it is hardly changed when flow rate arebetween 450--540m~3h~(-1), it is increased rapidly when flow rate is greater than 539m~3h~(-1).