Abstract: High-precision theoretical modelling of gravity field variations induced by multiple known mechanisms is a prerequisite for studying dynamic processes of the Earth's surface and interior through gravimetry. Temperature fields on the Earth and other celestial bodies, driven by factors such as solar radiation and magmatic eruptions, often exhibit periodic or step-like fluctuations. These thermal perturbations not only generate deformation fields but also disturb the gravity field. In this study, we employ a thermoelastic half-space model and solve the governing partial differential equations analytically to derive explicit expressions for the deformation and gravity changes induced by surface point and disk-shaped heat sources under periodic and step-like temperature fluctuations. The results demonstrate that gravity variations at the surface caused by thermoelastic effects are manifested solely as the free-air gradient due to the movement of gravimetric instruments with surface deformation, while the contributions from internal strain and Bouguer-layer surface displacement cancel each other at the first order. Finally, two representative examples are presented to illustrate the magnitude of thermoelastic deformation and its gravitational effects: (1) for periodic temperature fluctuations on the lunar surface, the resulting surface uplift is estimated to be at the sub-millimeter level, with gravity changes smaller than 1 μGal; (2) for a sudden temperature disturbance in the permanent lava lake of Mount Nyiragongo, assuming a magma lake with a radius of 400 m and a temperature increase of 40 K, the predicted stable thermoelastic vertical displacement at the center is about 10 cm and the associated gravity change is about 30 μGal.