Many of the previous studies have shown us that free shipping can increase customer desire to buy products and actual sales. But sometimes, the effect of free shipping plays a role on consumer’s consuming behaviors in different degree. We have encountered situations where consumers decide whether to buy products mainly based on whether it is free shipping or not, but sometimes the free shipping is just a small discount for consumers and cannot be used as a deciding factor for purchase intention. Shipping fees can sometimes be treated as a bundled service coming along with the product, also when occasionally shipping fees are more like a partitioned surcharge additionally attached with the product. So, it is very important for us to understand under what circumstances free shipping will have different effects on consumers. Through online questionnaire among 267 consumers, this paper starts from the point of consumer's need for products and demonstrates that free shipping can greatly and positively increase the purchase intention of low need product compared with high product, where the effect of free shipping on consumer’s purchase intention is not salient. Moreover, the paper considers the sensitivity of shipping charge as a mediator, explaining the connection between product need and free shipping effect. Conclusively, when people's need for products is high, people's sensitivity to shipping will decrease, resulting in reduced effect of free shipping on consumer’s desire of buying. On the contrary, when people's need for products is relatively low, people will be more sensitive and concerned about the shipping fees, under which circumstance when the product is free shipping, it will more obviously and increasingly have an effect on consumer’s purchase intention.