Abstract: In order to complete the monitor of ultra-broadband spectrum for solar radio burst, Yunnan Observatories have designed and developed 4 solar radio spectrometers with the frequency range of 15-80 MHz, 100-750 MHz, 600-4 200 MHz and 4-15 GHz, which are called decametric, metric, decimetric and resolution centimetric solar radio spectrometer, respectively. For the decametric solar radio spectrometer, the spectral resolution and temporal resolution have reached 7.6 kHz and 1 ms, respectively. For metric and decimetric, the spectral resolution and temporal resolution have reached 9.5 kHz and 10 ms, respectively. For the centimetric spectrometer, the spectral and temporal resolution have reached 76 kHz and 10 ms, respectively. Each spectrometer includes antenna system, receiver and digital spectrometer. In order to obtain a spectrum with ultra-high spectral resolution, the maximum word length of FFT is 262 144, which cannot be achieved by one-time FFT in FPGA, the parallel FFT algorithm is need. For the large word length of FFT, the data need to be transformed into a FFT with two small word length by doing a row decomposition and then parallel processing. In this paper, the algorithm is studied and simulated by using Matlab, then is applied to digital spectrometer. The test results of the digital spectrometer are good consistency with the simulation, indicating the successful application of the algorithm on the digital spectrometer. This paper introduces the composition of solar radio spectrometer and the method of implementing ultra-high resolution based on FPGA.