It is possible to observe slow light pulse based on transitions between Zeeman sub-levels of D1 line in rubidium atoms. In the experiment, when two laser beams with opposite circular polarizations (σ－ and σ+), called probing light which is weak and coupling light which is strong respectively, couple transitions between Zeeman sub-levels of D1 line F=2→F′=1 in rubidium atoms, electromagnetically induced transparency (EIT) with reduced absorption and enhanced dispersion is achieved in the atomic medium and simultaneously results in slow light. Influence of the coupling light intensity and pulse width of the probe beam on reducing the group velocity is investigated. The delay of probe pulse increases continually when decreasing the coupling beam power, which indicates more significant reduction in group velocity. The optical pulse width is smaller, the ratio of the light pulse delay and pulse width is larger, and separation of reference and probe light is larger.