Abstract: The aim of this study is to optimize the performance of the formaldehyde gas sensor is enhanced in the study.Micro formaldehyde sensor is based on a quartz substrate utilizing with Pt micro-heater to heat the sensing layer（NiO thin film）.When formaldehyde exists in the air,the electrical conductivity of the NiO layer increases and the resistivity decreases.The thickness of the NiO film is 0.34 μm,the response time is 6 sec,the sensitivity is 13.5 kohm/ppb and the lowest detection limit is 40 ppb.In the present study,to enhance its sensing performance,co-sputtering NiO/Al₂O₃,changing electrode shape and changing working temperature are considered.