Abstract: Non-isothermal viscoelastic fluid flow phenomena widely exist in nature and industrial productions, such as oil reservoir engineering, injection molding, etc. These flows generally exhibit a non-isothermal state. Accurate prediction of non-isothermal flow mechanism and complex rheological properties of viscoelastic fluid has important engineering application value. In this paper, an improved smoothed particle hydrodynamics (SPH) method is proposed for the numerical simulation of non-isothermal viscoelastic complex flow, in which the viscoelastic properties of the fluid are characterized by the eXtended Pom-Pom constitutive model. To improve the accuracy of simulation results, a kernel function gradient correction algorithm is adopted. To enforce the boundary conditions flexibly, a boundary treatment method combining boundary particles and virtual particles is developed. To eliminate the tensile instability in the flow process, the particle migration technology is applied. The improved SPH method is used to numerically simulate the impact of a droplet on the solid wall and injection molding of an F-shaped cavity. The effectiveness of the improved SPH method in solving the non-isothermal viscoelastic fluid is verified by comparing the SPH results with those obtained by the Basilisk software. Good agreement between these two numerical solutions is achieved. The numerical convergence of the improved SPH method is evaluated by using several different initial particle spacings. The different flow characteristics of non-isothermal flow compared with isothermal flow are investigated. It is found that the introduction of temperature leads to stronger contraction behavior of droplet. The influences of some different thermal rheological parameters such as the Péclet number, the Reyonlds number, the Weissenberg number, the solvent viscosity ratio, the anisotropy parameter, the relaxation time ratio and the molecular chain arm number on the flow process are deeply analyzed. The numerical results show that the improved SPH method proposed in this paper can accurately and stably describe the heat transfer mechanism, complex rheological properties, and free surface variation characteristics of non-isothermal viscoelastic fluid.