The primary objective of pneumatic conveying system design is to achieve energy-efficient, continuous, and stable material transportation, where the system performance is fundamentally governed by pressure drop characteristics. Although dense-phase pneumatic conveying exhibits superior transport efficiency and energy-saving potential compared to dilute-phase systems, its industrial application is constrained by complex gas-solid flow dynamics. These dynamics induce significant pressure fluctuations and unstable pressure drops, particularly in the horizontal conveying section downstream of the feeding outlet, which must be prioritized in system optimization. This study employs carbon black masterbatch as the experimental material and utilizes a pneumatic conveying cycle test bench to investigate the pressure drop characteristics in the horizontal feeding outlet section of the dense-phase system, focusing on steady-state pressure drop characteristic. Experimental protocols involve modulating rotary valve frequencies to generate solid-gas ratios ranging from 12 to 32, enabling the acquisition of pressure drop variation data in the feeding outlet section. Further analysis and prediction of total acceleration section pressure drop are conducted using empirical formulas and response surface methodology (RSM). The results show that the pressure drop of filling shoe is dominant in the pressure drop change of the filling shoe acceleration section L12, and both of them increase approximately linearly with the increase of solid-gas ratio. In the feeding outlet acceleration section L23, the prediction model of the pressure drop calculation coefficient (solid-phase friction coefficient) model is established by response surface method. When the solid-gas ratio is 12~26, the relative error between the model predicted pressure drop and the experimental value is within 15%. However, when the solid-gas ratio is 26~32, the pressure drop exhibits unstable fluctuation characteristics, and the prediction method based on the additional pressure drop method is no longer applicable.