In this work, multifunctional polystyrene@chitosan@gold nanoparticles-Fe3O4 nanoparticles-folic acid/indocyanine green (PS@CS@Au-Fe3O4-FA/ICG) nanocomposites that can integrate diagnosis and therapy into one nanoplatform was fabricated. The constructed PS@CS@Au-Fe3O4-FA/ICG nanocomposites possessed excellent computed tomography, magnetic resonance and fluorescence imaging performances which could be used to diagnose tumor and monitor the nanocomposites' localization in vivo. Moreover, PS@CS@Au-Fe3O4-FA/ICG nanocomposites can be delivered in a targeted manner to cancer cells by folic acid in a receptor-mediated way, and tumor growth could be efficiently inhibited, even completely ablated, under NIR irradiation. That is, the constructed PS@CS@Au-Fe3O4-FA/ICG nanocomposites had great potential for computed tomography, magnetic resonance and fluorescence imaging performances, which could be used to diagnose tumors and to monitor local therapy and fluorescence imaging-guided targeted therapy of cancer cells using nanocomposites.