A radar Electronic Support Measures (ESM) system performs two functions, warning of impending emitters and surveillance to determine the radar activities. Automatic radar ESM system consists of a passive radar receiver which receives emissions from other platforms, measures the parameters of each received pulse and a deinterleaver that sorts the intercepted pulses to enable determination of the individual radar parameters. These parameters are compared with the stored parameters of known radars to identify the intercepted emitter type. Consequently the threat evel and the optimum jamming program for the intercepted emitter could be derived. This paper concentrates on emitters deinterleaving in case of high data rate of about 106 pulse/second. Emitter deinterleaving involves sorting and segregating the received radar pulses into separate cells each cell is associated with a single emitter Additional parameters such as PRI, and antenna scan pattern could be evaluated for each cell. A proposed deinterleaving algorithm, which depends on the mono-pulse parameters, is presented. Both the physical and analytic behaviors of this algorithm are examined through computer simulations.