The application of piezoelectric ceramics at high temperature is limited because they can’t have both high piezoelectric coefficient and high Curie temperature. While, BiScO3-PbTiO3-based piezoelectric ceramics possessing high Curie temperature and piezoelectric properties simultaneously have drawn increasing attention due to their potential applications at high temperature. Here, we reported a novel compositional design of (1-x)[0.36BiScO3-0.64PbTiO3]-xBi(Sn1/3Nb2/3)O3 (abbreviated as BS-PT-xBSN). BS-PT-xBSN ceramic samples were synthesized by conventional solid state reaction method. According to the ternary phase diagram of BS-PT-xBSN ceramics brought up in this work, the morphotropic phase boundaries (MPB) were confirmed, which is located in the vicinity of x = 0.02. It canbe identified that the x = 0.02 sample near MPB has the optimal electric performance which are giant piezoelectric coefficient (d33 ∼ 450 pC/N, higher 18% than undoped samples) and high Curie temperature (Tc ∼ 368 °C) as well as large remant polarization (Pr ∼ 46.6 μC/cm2). In addition, the variation of Pr is 3% in the temperature range of 30-180 °C and the depolarization temperature of x = 0.02 ceramics is about 280 °C. Structural analysis such as in-situ PFM and TEM confirms that giant piezoelectricity and depolarization temperature are attributed to the appearance of nano-domain and complexity of domains as well as the stable domain configuration. This work not only reveal the high potential of BS-PT-xBSN for high-temperature piezoelectric applications but also open up a feasible approach to design new high-temperature piezoelectric ceramics.