A computer-implemented method for identifying a fluctuation start point in a total current waveform, the total current waveform being a waveform of a coil current in a control rod drive mechanism of a nuclear power plant, wherein the method uses a computer to perform steps comprising: obtaining the total current waveform, identifying and extracting a fluctuant waveform segment in the total current waveform and a stationary waveform segment that is close to and located in front of the fluctuant waveform segment; and calculating a mean value from each data point in the stationary waveform segment, and a difference value A between each data point and the mean value; and calculating a value of each data point in the fluctuant waveform segment; characterised in that: step further comprises: calculating a difference value B between two adjacent data points; calculating an average fluctuation limit value according to the difference value A; and calculating an adjacent fluctuation limit value according to the difference value B; step further comprises: sequentially searching forward from a front end of the fluctuant waveform segment and calculating a difference value C between each data point and the mean value, and taking a current data point as a first data point once the difference value C exceeds the average fluctuation limit value; and the method further comprises: searching backward along the fluctuant waveform segment from the first data point and calculating a difference value D between each data point and a previous data point, and marking a current data point as a fluctuation start point once the difference value D does not exceed the adjacent fluctuation limit value. obtaining the total current waveform, identifying and extracting a fluctuant waveform segment in the total current waveform and a stationary waveform segment that is close to and located in front of the fluctuant waveform segment; and calculating a mean value from each data point in the stationary waveform segment, and a difference value A between each data point and the mean value; and calculating a value of each data point in the fluctuant waveform segment; characterised in that: step further comprises: calculating a difference value B between two adjacent data points; calculating an average fluctuation limit value according to the difference value A; and calculating an adjacent fluctuation limit value according to the difference value B; step further comprises: sequentially searching forward from a front end of the fluctuant waveform segment and calculating a difference value C between each data point and the mean value, and taking a current data point as a first data point once the difference value C exceeds the average fluctuation limit value; and the method further comprises: step further comprises: calculating a difference value B between two adjacent data points; calculating an average fluctuation limit value according to the difference value A; and calculating an adjacent fluctuation limit value according to the difference value B; calculating a difference value B between two adjacent data points; calculating an average fluctuation limit value according to the difference value A; and calculating an adjacent fluctuation limit value according to the difference value B; step further comprises: sequentially searching forward from a front end of the fluctuant waveform segment and calculating a difference value C between each data point and the mean value, and taking a current data point as a first data point once the difference value C exceeds the average fluctuation limit value; and sequentially searching forward from a front end of the fluctuant waveform segment and calculating a difference value C between each data point and the mean value, and taking a current data point as a first data point once the difference value C exceeds the average fluctuation limit value; and the method further comprises: searching backward along the fluctuant waveform segment from the first data point and calculating a difference value D between each data point and a previous data point, and marking a current data point as a fluctuation start point once the difference value D does not exceed the adjacent fluctuation limit value.