Physiological measures indexed by fixation frequency and total fixation time,task performance based on N-back accuracy,subjective assessment based on NASA Task Load Index(NASA-TLX)were used to measure the Mental Workload(MW)in different levels which were induced by vision-related flight task combined with auditory cognitive load.16 healthy novice pilots were recruited to complete a monitoring task based on Head-Up Display(HUD)and an auditory N-back task which was used to manipulate the Mental Workload Level(MWL)in flight simulation environment.In our experiment,fixation frequency,average saccade time,blink rate and average pupil diameter were sensitive to MW.What’s more,a comprehensive assessment method of pilot mental workload based on various measures was advocated.At last,a Fisher projection function based on the Fisher discrimination method and a three-level discriminate model established by the Bayes discrimination method were built up,the original validation and cross-validation methods of both models were97.92% and 95.83% respectively,which could discriminate various Mental Workload Levels(MWLs)ideally.:mental workload;fixation frequency;bayes discrimination method Physiological measures indexed by fixation frequency and total fixation time, task performance based on N-back accuracy, subjective assessment based on NASA Task Load Index (NASA-TLX) were used to measure the Mental Workload (MW) in different levels which were induced by vision-related flight task combined with auditory cognitive load.16 healthy novice pilots were recruited to complete a monitoring task based on Head-Up Display (HUD) and an auditory N-back task which was used to manipulate the Mental Workload Level (MWL) in flight simulation environment. In our experiment, fixation frequency, average saccade time, blink rate and average pupil diameter were sensitive to MW. What’s more, a comprehensive assessment method of pilot mental workload based on various measures was advocated. At last, a Fisher projection function based on the Fisher discrimination method and a three-level discriminate model established by the Bayes discrimination method were built up, the original verification and cross-validatio n could both discriminate various Mental Workload Levels (MWLs) ideally .:mental workload; fixation frequency; bayes discrimination method