A laser induced breakdown spectroscopy analytical system was established by using a pulsed 1064 nm Nd:YAG laser and a portable fiber optical spectrometer. The emitted spectra of the laser induced soil plasma were recorded along with the variation of experimental parameters. By using the AlⅡ 422.68 nm as the analysis line, the effects of the laser energy and data acquisition delay time on the spectrum characterizations of soil plasma emission were investigated in detail. Generally, at a fixed laser energy, the signal intensity, background and noise of the spectrum decrease with a longer acquisition time delay, while the signal to noise ratio (SNR) first increases to a maximum and then decreases. And at a fixed data acquisition time delay, the signal intensity and noise of the spectrum increase with the increase of laser energy, but the background and SNR first increase to a maximum and then decrease. For specific laser energy, the SNR can be optimized at a selected suitable data acquisition time delay, and the optimal time delay will increase with increased laser energy. Based on the combination effects of laser energy and data acquisition time delay, the optimized parameters of the system are 120 mJ for the laser energy and 1.5 μs for the acquisition delay time.