The influence on the motion of single solid particles in a Newtonian fluid by melting and convection is direcly simulated. The fluid motion is computed from the conservation laws. Density and viscosity change with fluid temperature, and the particle moves according to the equation of motion of a rigid body under the action of gravity and hydrodynamic forces arising from the motion of the fluid. In the process of melting, a distinctive morphology develops due to the different heat fluxes around the particle's surface, and the thermal gradient determines the melting rate. The phases are coupled by the fluid-particle mutual force , force moment and the boundary conditions. In our study, two different situations are carried out, which are sedimentation in isothermal fluid without thermal convection and melting; sedimentation with thermal convection and melting, two double particles are simulated separately. The results show that the vortex shedding arising by the natural convection, mass losing by melting and melting morphology change the sedimentation velocity and induce horizontal oscillation.