Novel NASICON-type structural Li1.3Al0.3Ti1.7SixP5(3-0.8x)O12 (LATSP) solid electrolytes are synthesized by spray-drying combined with sintering methods, and the corresponding physicochemical properties are investigated by X-ray diffraction, Field emission scanning electron microscope, Fourier transform infrared spectrometer and X-ray photoelectron spectroscopy. The targeted LATSP powders present uniform cube-like morphology and excellent crystallinity, in which the LATSP-0.05 solid electrolyte exhibits a high ionic conductivity of 1.053 E-4 S cm−1 and a low activation energy of 0.44 eV at 25 °C as well as a high compaction density of 2.892 g cm−3 when the content of Si doping retains 5% vs. the molar ratio of the pure Li1.3Al0.3Ti1.7(PO4)3. Furthermore, the assembled LiCoO2/LATSP-0.05/Li all-solid-state coin cell can achieve a relatively high initial discharge specific capacity of 116.2 mAh g−1 at 0.1C and possess outstanding cycle and rate performance compared to other cells at room temperature. These results show that the novel LATSP-0.05 solid electrolyte with NASICON-type structure is expected to widely employ in the field of all-solid-state lithium ion batteries.