Based on Social Exchange Theory and Motivation Crowding Theory, we study the motivations of consumers to spread e-WOM by benefit factors and cost factors. Meanwhile, we brought the motivation crowding effect into the analysis model, and discussed the effect of extrinsic motivation on intrinsic motivation and internalized extrinsic motivation. Through empirical analysis in China, we find that altruism, product involvement, self enhancement have significant positive influence on the intention to spread e-WOM, while execution cost has a significant negative influence on the intention, and economic incentive has significant crowding in effect on altruism, product involvement and self enhancement.