According to the body-specificity hypothesis, people will associate positive and negative emotional valence with the relative fluency of the left or right responding hand. Prior studies have shown that temporary changes in the fluency of the responding hand can influence the association of emotional valence with left or right, even under circumstances of action observation. But the reason why this change occurs is still controversial. The purpose of the present study was to replicate this finding and to identify the underlying mechanism. Experiment 1 duplicated a modified paradigm "Bob goes to the zoo" to verify the existence of space-valence association for Chinese right-handers. The results indicated that they had the same pattern of right-good/left-bad. However, after action training and observation in Experiment 2 that reduced the fluency of the right hand temporarily, both actors' and observers' space-valence associations were reversed as well. However, when observers' potential motor capacities were constrained by binding their responding hands behind them (Experiment 3) or in front of them (Experiment 4), the observers associated the positive affect with their dominant right hand instead of the left hand in Experiment 3, whereas the observers in Experiment 4 still showed the same association pattern as the actors and the observers in Experiment 2. This study provides further evidence that the effect of alternative motor fluency on space-valence association in the observer is mainly modulated by the connection between the outcomes and space, with body posture also influencing the association.