Based on widely used photoacoustic imaging (PAI) and photothermal properties of polydopamine (PDA), a multifunctional Gd–PDA-Ce6@Gd-MOF (GPCG) nanosystem with a core–shell structure and strong imaging ability was constructed. Benefitting from the metal–organic framework (MOF) structure, GPCG nanoparticles (NPs) showed enhanced magnetic resonance imaging (MRI) ability with high relaxation rates (r₁ = 13.72 mM⁻¹ s⁻¹ and r₂ = 216.14 mM⁻¹ s⁻¹). The MRI effect of Gd ions combined with the PAI effect of PDA, giving GPCG NPs a dual-modal imaging ability. The core, mainly composed of PDA and photodynamic photosensitizer chlorin e6 (Ce6), achieved photothermal/photodynamic therapy (PTT/PDT) synergistic performance. Besides, to overcome the unexpected release of Ce6, the MOF shell realized pH-sensitive release and a high local concentration. Through in vivo studies, we concluded that GPCG NPs show a good inhibitory effect on tumor growth. In conclusion, we successfully obtained a GPCG theranostic nanoplatform and paved the way for subsequent design of imaging guided therapeutic nanostructures based on metal-doped PDA.