This paper reports the observation of a spectrum on an atomic beam in slow-microwave fields using the optical pumping. The spectrum is given in standing microwave fields when the slow-wave factors of helix structures are 5.20 and 10.67 respectively. Doppler shift varying with the slow-wave factor is observed experimentally, and the influece of the field polarization on the spectrum is discussed. The boardening of the spectral line in the spectrum when the helix stucture is perpendicular to the atomic beam is also observed and discussed.