Abstract:  Frank-Hertz experiment has substantial physics content，and the optimization of its experimental conditions has been extensively discussed in the past.It is a right choice to clearly understand experimental physics by introducing experimental optimizing method and its physical judgment.The preliminary experimental results are obtained by using default parameters provided by equipment manufacturer.On the basis of measurement principles，the collector potential is set to be close to but less than the experimental excitation potential.Then，the filament voltage (current) is appropriately adjusted according to the influence of filament temperature on hot electron emission density.Finally，the first grid potential is changed and its influence is observed.The experimental optimization level is quantitatively evaluated with an indicator defined as the mean and standard deviation of collector current values at the peak and the valley.The accurate experimental results can be obtained on the optimal experiment condition.

Key words:  Frank-Hertz experiment, excitation potential, optimal experiment conditions, physical foundation