The parameters of seawater, such as temperature can be detected based on the detection of Brillouin scattering signal. Because Brillouin frequency shift is a function of two variables, temperature and salinity, the precise measurement about the two independent variables by Brillouin frequency shift is impossible. It is found power of Brillouin scattering signal is also a function of those two variables, so the method to simultaneously measure temperature and salinity by measuring the frequency shift and power is proposed and the synchronous measurement about temperature and salinity is realized.