Brain tumors, especially the most prevalent and aggressive glioblastoma, remain among the deadliest of all types of cancer due to inefficient theranostic options. They have a limited therapeutic window because of physiological barriers such as the blood-brain barrier (BBB), blood cerebrospinal fluid (CSF) barrier and interstitial fluid (ISF) that restrict the penetration of imaging probes and therapeutic drugs. In order to achieve more accurate brain tumor diagnosis and better therapeutic effects, many strategies have been explored; among them multifunctional nanoparticles offer a novel and potential opportunity depending on their size effects, and their optical, magnetic, photodynamic and other properties. After modification, nanoparticles can cross the BBB and specifically accumulate in the tumor site, thereby achieving accurate tumor imaging and drug release. This review is focused on various types of nanoparticles that are being used for improving nano-carriers of diagnostic and therapeutic agents into brain tumors and also provides a concise summary of various multifunctional theranostic strategies, particularly in clinical applications. In this manner, we provide evidence for the key role of nanoparticle based diagnosis and therapy systems in brain tumors.