Abstract: In order to study the pressure drop characteristics of high-pressure dense phase pneumatic conveying of mix- ing coal with coal liquefaction residue raffinate,this paper investigates the pressure drop characteristics of a horizontal straight pipe on a pneumatic conveying device with a maximum operating pressure of 6 MPa at the conveying pipe di- ameter of DN25 and DN15. The experimental study has been carried out under multiple operating conditions,and the results show that the blending extract residue has a significant effect on both the magnitude and fluctuation of the pres- sure drop of the horizontal straight pipe. The hydraulic smooth pipe calculation formula is used to calculate the gas phase friction coefficient,and the calculated pressure drop value in the high velocity region ( >8 m / s) of gas phase shows a large error between the calculated and measured value. The wall roughness of DN25 and DN15 pipes obtained by least squares regression is 0. 015 mm and 0. 013 mm respectively,and the calculation error of the gas phase pres- sure drop is less than 10% . The particle phase pressure drop is obtained by dimensional analysis,and the error between the calculated value of pressure drop of M1 and M2 and the experimental value is within 30% . At low Froude number,the particle phase friction coefficient of M2 is significantly higher than M1,and the two values tend to be i- dentical under high Froude number. The pressure drop of gas phase is a non-negligible part of the total pressure drop. As the superficial gas velocity increases,the proportion of particle pressure drop gradually decreases. As the solid-gas ratio increases,the proportion of pressure drop of particle phase increases.