Laser-induced breakdown spectroscopy (LIBS) has the advantages of no sample pretreatment, simple operation, rapid detection, etc.,and it has been applied in many fields. In this experiment, femtosecond laser-induced breakdown spectroscopy (Fs-LIBS) was developed, using a femtosecond laser with a wavelength of 800 nm and a pulse width of 100 fs as the excitation light source and a gated ICCD as the detector. When LIBS detects bulk liquids, problems such as liquid fluctuations and splashes will occur, and the signal will be poor. In this experiment, NaCl standard solution jet flow was used to test and optimize the system, and Na(Ⅰ) 589.0 nm was chosen as the analysis line. The evolution of the LIBS emission spectrum after the femtosecond laser excitation was investigated. The maximum Na atom emission and the best signal-to-background ratio were obtained after 40 ns of laser excitation. It shows that femtosecond time-resolved LIBS can effectively eliminate the influence of broadband background emission and more efficiently detect the target. The effects of laser excitation power, ICCD gate width, the distance between the laser focus to sample surface on LIBS intensity and signal-to-noise ratio were studied and optimized. At the best experimental parameters: 40 ns delay time, 100 mW excitation power, 5 s gate width, and laser focus right on the front surface of the sample, the LIBS spectrum and Na content of a seawater sample were tested, and the detection limit of Na for NaCl standard solution was determined to be 0.98 mg·L-1. The experimental results show that the LIBS technology meets the requirements of rapid and real-time detection of elements, can be used to study the plasma dynamics evolution process and achieve a qualitative and quantitative elements analysis.