Fluid wave code communication is used for layered water injection intelligent monitoring system, but the mechanism of fluid pressure signal generation and wave code transmission has not been known. In this paper, based on the fluid energy equation of steady flow, the mathematical model of the generation and transmission process of fluid pressure signal was established. The pressure signals and influencing factors generated by the ground electric control valve and the downhole flow control device were studied, and the transmission mechanism of the signal in the water injection pipe was revealed. Studies have shown that ground and downhole pressure signals are generated by flow changes caused by changes in the opening degree of the ground valve and the downhole flow control device. The pressure signal amplitude is affected by fluid, water pipe network, water injection pipe or wellbore parameters, fluid device structure and fluid control parameters. The influence of the signal along the water injection pipe is the induction of the flow change caused by the change of the opening degree of the electric control valve, the length of the water injection pipe has no effect on the downlink transmission of the ground signal, but has a certain influence on the uploading of the downhole signal. Numerical calculations show that the maximum flow rate of the water injection pipe and the variation of the resistance coefficient of the electric control valve have a great influence on the amplitude of the pressure signal. The larger flow rate and the variation of the resistance coefficient can generate a larger signal amplitude, which is beneficial to the signal transmission, signal detection and signal processing. The research in this paper has a certain theoretical guidance for the design and performance improvement of fluid wave code communication system.