Abstract: It is very important to research the primary productive forces of the ancient sea in order to attempt to find a solution for the current energy and climate problems. At present, all of the proxies to estimate the primary productive forces of the sea have certain limitations. In this paper, a new proxy of Br is introduced and the description of establishing a new method for Pyrohydrolysis-Catalytic Spectrophotometry to digest marine carbonate rock and determine Br. The Permian marine carbonate rocks were decomposed by pyrohydrolysis, the Br was trapped by NaOH solution (0.1%) and measured by Catalytic Spectrophotometry. The optimal experimental conditions for pyrohydrolysis and the optimal wave length for Catalytic Spectrophotometry are described. The recovery rates were in the range of 97.5%-101.6% with RSD (n=10) from 1.2% to 3.6%. This experimental technique is highly suitable for marine carbonate rock samples due to its use of commonly available equipment, simple operation, short operational process and low cost.