〖HJ1mm〗A reasonable and efficient femtosecond laser fast response confocal altimetry cascade control processing system is established for the precision focus control of infrared focal plane detector in the femtosecond laser scratching techniques.On the basis of ensuring the stable height measurement and accurate control of the femtosecond laser,there are also two key points need to be deeply studied.The distortion of the curve has been reduced by using altimeter and median filter after optimum fitting.The following precision of piezoelectric ceramics is optimized by the single axis position based triggering and PI control.The experimental results show that the system can achieve good performance.For different sizes of wafers,the overall follow up variance is 0.6μmwhen processed at 800mm/s speed,maximum error 1.1μm；when processing at a speed of 1000mm/s,the overall follow up variance is 0.9μm,maximum error 1.4μm.This method can effectively improve the precision of focus control in high speed femtosecond laser machining,so as to ensure the edge quality of infrared focal plane array (IRFPA) detector,and to increase product yield and reduce cost.