Abstract: A home-made mass spectrometer specially designed for studies of laser plasma reactions is in- troduced in this paper. In this instrument, pulsed laser beam of high energy density is focused on the sample which consists of the mixed reagent in solid state. The mass spectra of both positive and negative ions in laser plasma are recorded on two time-of-flight mass spectrometers coincidently in situ. As the samples of the reactions, the experimental results of reactions among sulfur, phosphrous, silver and niobium are described. Breif discussions and analysis of these results are also presented in this paper.