Abstract: In this paper，an example of calculating the probability amplitude in momentum representation and

the probability distribution of the electron momentum in hydrogen atom in quantum mechanics course by Mr. Zhou

shixun is discussed. The method of calibration of momentum direction in the solution is questioned. For calculating

probability amplitude of momentum，the method is not universal since the representation depends on the selection of

momentum direction. Only for the s-states which have spherical symmetry and are independent of momentum direction

since the spherical harmonic function in probability amplitude is independent of momentum direction，this

method has no effect on the representation. Furthermore，for calculating the probability distribution of the electron

momentum，the calculation requires integrating the angular quantity of momentum，it is not appropriate to calibrate

the momentum direction before the calculation.

Key words: hydrogen atom, momentum representation, momentum direction