Poly(ethylene oxide) (PEO) polymer electrolyte has been regarded as a potential solid electrolyte which can be applied in all-solid-state lithium-ion batteries (ASSLIBs). Nevertheless, low electrochemical properties and poor electrolyte/Li anode interfacial stability hinder its further application. In our work, the Li1.3Al0.3Ti1.7(PO4)(3) (LATP) nanomaterials with Nasicon structure have been synthesized using a simple solvent-thermal method, followed by being embedded into PEO polymer to form LATP filled PEO solid composite electrolytes. Effects of LATP content and particle size on electrochemical performances of solid electrolytes have been studied. By adjusting the calcination temperature, the uniformly distributed Nasicon-type LATP powders with different sizes can be obtained. The electrochemical properties of PEO polymer electrolyte have been effectively enhanced by filling LATP nanoparticles. The composite electrolyte filled with 5 wt% LATP particles calcined at 850 degrees C exhibits a high ionic conductivity of 5.24x10(-4) S cm(-1) at 55 degrees C, which has a high electrochemical stability window of over 5 V versus Li/Li+ and a superior interfacial stability with Li metal. A LiFePO4/Li ASSLIB fabricated with the optimum composite electrolyte shows the excellent rate capability, and its discharge capacities at 0.2C, 0.5C, 1C, and 2C are 151.97, 151.56, 145.51, and 128.02 mAh center dot g(-1). Moreover, the discharge capacity of the cell decreases from 151.69 to 130.53 mAh center dot g(-1) after 100 charge-discharge cycles at 0.5C rate, and the corresponding capacity retention is 86.05%. These results demonstrate that LATP nanoparticles obtained via the solvent-thermal method are the alternative fillers for PEO polymer electrolyte.