The dynamic spectral observation at decametric wavelength is important to study solar radio physics and space weather. However, the observing system is difficult to observe with high sensitivity at this band due to the fact that the system temperature is dominated by the sky background noise and the antenna is difficult to design with high gain. An effective solution to improve the sensitivity is constructing an antenna array based on the beamforming method. Accordingly, we develop a decametric solar radio spectrometer system based on a 4-element beamforming array. The system consists of four antennas, an 8-channel analog receiver and a digital receiver. We use the true time delay to implement the beamformer and the classical FFT method to perform spectrum analysis in the digital receiver. Operating at a frequency range of 25-65 MHz with dual-circular polarizations, the system provides high resolution dynamic spectrum with spectral resolution of & SIM;12 kHz and temporal resolution of & SIM;5.3 ms (typical). Tens of solar radio bursts have been observed successfully during the period of the trial observation, demonstrating the system's ability to detect fine structures with high spectral and temporal resolution. In this article, we present the design, implementation, and initial observational results of the decametric solar radio spectrometer system in detail.