Based on the development of MEMS technology, this paper studies a constant temperature difference (CTD) thermal distributed flow sensor known for its low startup flow, high accuracy, and repeatability. A theoretical model with insulated microgrooves and cavities is established, confirming that stabilizing the temperature difference between the heating resistor and the ambient environment improves sensor accuracy. According to Thomas’s theory, flow rate is derived from the temperature difference detected by upstream and downstream sensing resistors. A dedicated CTD circuit is designed and tested, showing excellent linearity (R² ? 0.9954) and low temperature- dependent error (<0.11%), effectively maintaining the set temperature difference within 0–50°C.