Abstract: For the thermal residual stress and deformation phenomenon of 3D printing parts, two key factors of platform and dynamic cooling gradient were introduced, and the analytical expressions of thermal residual stress and deformation were established and verified by numerical examples. The results show that the calculation was consistent with the actual situation after introducing the platform and dynamic cooling gradient. The greater the difference between the platform temperature and the forming temperature, the greater the cooling gradient, the thermal residual stress and the deformation. The platform removal time after printing had no effect on the thermal residual stress and deformation level, but ignoring the influence of the platform caused a large error in the analytical solution. Keeping the platform at a constant temperature significantly reduced the thermal residual stress, and the closer the holding temperature to the printing temperature, the lower the thermal residual stress.