Abstract: This paper presents the study on the enhancement mechanism of laser-induced breakdown spectroscopy on cobalt sample with double femtosecond pulse. The double-pulse experiments were carried out in the collinear beam geometry in air. The influence of the delay between the two collinear laser pulses was investigated by changing the pulses path length. In cases of no delay between the two pulses, the laser-induced breakdown spectroscopy is equivalent to that induced by a single pulse laser with energy equals to the sum of the double collinear pulse energy. The obtained results show that with an optimized delay, the double-pulse laser-induced breakdown spectroscopy has a very clear enhancement comparing with the single-pulse laser induced breakdown spectroscopy. In addition, the dependence of the electron temperature obtained by linear Boltzmann method on the pulse interval was investigated. The experiment shows that the dependence of spectral enhancement factor on the pulse interval is the same as that of the electron temperature, both of them go through two obvious changing processes. Analysing by the Boltzmann equation, we draw the conclusion that the spectral signal enhancement depends on the electron temperature.