When the vacuum preloading (VP) is used to consolidate the engineering waste slurry, there are several problems, such as the clogging of prefabricated vertical drain (PVD), formation of the soil columns and the attenuation of vacuum degree with depth, resulting in non-uniform consolidation. Considering the characteristics of prefabricated horizontal drain (PHD) in the treatment of soft soil foundation by VP method, a vacuum preloading method combined PHD with PVD (PHD-PVD-VP) is proposed to treat the slurry. Through four groups of large-scale indoor model tests, the drainage, settlement and pore water pressure during consolidation of engineering waste slurry were monitored, combined with the micro pictures of drainage board filter membrane obtained by scanning electron microscope, the consolidation effect of PHD-PVD-VP on engineering waste slurry under different initial PHD vacuum pressures was analyzed. The test results show that the PHD-PVD-VP reduces the radial movement rate of soil particles, delays the formation of "soil column", alleviates the silting effect of soil particles embedded in the filter membrane of drainage plate, and improves the overall consolidation effect of soil; initial PHD vacuum pressure of 40 kPa makes the drainage and consolidation effect of PHD-PVD-VP on engineering waste slurry the best, the average water content and vane shear strength of the treated soil were 40.9% and 25.5 kPa respectively. It not only effectively avoids the clogging of PHD and PVD, but also improves the uniformity of soil. Combined with the microstructure analysis, it is found that the initial PHD vacuum pressure affects the clogging of PHD and PVD filter membranes simultaneously, so as to affect their drainage performance. The initial PHD vacuum pressure of 40 kPa gives full play to the drainage performance of the two drainage boards.