Abstract: For distributed aperture coherent radar with cooperative architecture and pulse trains, the signal mode in fully coherent work mode is proposed firstly. Then the analysis formula of output Signal-to-Noise Ratio gain (oSNRg) is derived, and the performance bound of oSNRg is developed by using polynomial fitting based on Cramer-Rao Bounds (CRB) of coherence parameters estimation. It is concluded that more transmitters or pulses make higher oSNRg. However, as the number of receivers increase, if the input SNR is high sufficiently, the oSNRg will gradually improve; if not, it will worsen. Finally, numerical examples demonstrate the validity of the theoretical results.