Bioremediation experiments of polycyclic aromatic hydrocarbon (PAHs) using ryegrass (Lolium perenne), a turfgrass in urban landscapes, were carried out aiming to explore the ryegrass-assisted degradation in an actual PAH-contaminated urban soil and the phytotransformation pathways of PAHs within plants. Dynamics of plant-assisted degradation of 15 PAHs in pot soils were recorded over 100-day cultivation, and at the end, the accumulation of PAHs in ryegrass was investigated. Ryegrass with phenanthrene exposure was cultured hydroponically to investigate the phytotransformation intermediates using gas chromatography–mass spectrometry and ultra-performance liquid chromatography coupled to high-resolution mass spectrometry. Overall, dissipation of PAHs in soils exhibited an initial fast and subsequent slow degradation pattern. Eventually, on average, 55.7% and 47.1% of $$\sum {PAHs}$$ were removed in the planted and unplanted soils, respectively, with the high-molecular-weight PAHs highly eliminated particularly. Plant growth resulted in 4.8–11.1% more $$\sum {PAHs}$$ removed from soil compared to the plant-free controls. The PAHs all exhibited the bioconcentration and translocation factors below 1. The mass balance calculation showed that plant uptake accounted for < 1% of the dissipation increase while plant-promoted microbial biodegradation made the dominant contribution. A total of 7 metabolites were tentatively identified based on which possible transformation pathways were proposed. The results indicated that ryegrass may act as a metabolic sink for aqueous PAHs while microbes play a dominant role in soil PAH dissipation via biodegradation. The results may pave the path for a scientific, safe, and effective implementation of landscape configuration to ameliorate urban soil pollution.