The flow of six kinds of fresh concrete under different flow rates and lubrication layer thickness (T LL) values in the horizontal pipe was numerically simulated. The influence of the T LL on the pressure per unit length (P L) was analyzed. It was determined that the formation of the lubrication layer (LL) significantly reduces the P L in concrete pumping. As the T LL increased, the P L decreased. However, the degree of reduction in the P L gradually decreased as the T LL increased. Relating the simulated P L with the experimental P L, the size of the T LL was obtained, which was between 1 and 3 mm. The minimum and maximum were 1.23 and 2.58 mm, respectively, and the average value was 1.97 mm. The strength (S24, S50), the size of the aggregate (A10, A20, A25), and the flow rate of pumping all affected the T LL. The type of fresh concrete and the flow rate of pumping significantly affected the P L, which impacted the T LL. However, the T LL also impacted the P L. Finally, this made the T LL change within a certain range. When P L > 14,000 Pa/m, 2 mm < T LL< 3 mm; on the other hand, 1 mm < T LL< 2 mm. Therefore, we can use CFD to simulate the flow of all types of concrete in the actual pumping pipeline with a T LL of 2 mm to obtain their pumping pressure and guide the actual construction. Abstract The flow of six kinds of fresh concrete under different flow rates and lubrication layer thickness (T LL) values in the horizontal pipe was numerically simulated. The influence of the T LL on the pressure per unit length (P L) was analyzed. It was determined that the formation of the lubrication layer (LL) significantly reduces the P L in concrete pumping. As the T LL increased, the P L decreased. However, the degree of reduction in the P L gradually decreased as the T LL increased. Relating the simulated P L with the experimental P L, the size of the T LL was obtained, which was between 1 and 3 mm. The minimum and maximum were 1.23 and 2.58 mm, respectively, and the average value was 1.97 mm. The strength (S24, S50), the size of the aggregate (A10, A20, A25), and the flow rate of pumping all affected the T LL. The type of fresh concrete and the flow rate of pumping significantly affected the P L, which impacted the T LL. However, the T LL also impacted the P L. Finally, this made the T LL change within a certain range. When P L > 14,000 Pa/m, 2 mm < T LL< 3 mm; on the other hand, 1 mm < T LL< 2 mm. Therefore, we can use CFD to simulate the flow of all types of concrete in the actual pumping pipeline with a T LL of 2 mm to obtain their pumping pressure and guide the actual construction. Keywords: fresh concrete; pressure per unit length; horizontal pipe; simulation