An automobile hot-film air flow sensor is deposited with platinum by sputtering method, patterned by photoresisted lift-off method, annealed in $1,000^{circ}C$ and passivated with PI-2723. The TCR of the fabricated hot-film is about $3500;ppm/^{circ}C$. In the experiment, the output voltage of the sensor is in proportional to the fourth power root in the air mass flow range of 300 kg/h. The error in the full flow range is about ${pm}0.7%$. In the range of air temperature of $-20^{circ}C{sim}120^{circ}C$, the error is about ${pm}1%$ that is ${pm}2%$ lower than that of the reference sensor. Therefore, the fabricated hot-film air flow sensor satisfies the specification for automobile. Lower temperature error of the sensor provides to control the precise air/fuel ratio of automobile engine and results in improvement of a fuel mileage and the less amount of toxic gases emitted by automobile.