Economic relationships between business units based on geographi Ultra-low-price tour (ULPT) is a trap that some travel agencies use to attract cost-sensitive travelers by offering an extremely low price and making them spend much more money during the trip. Government has taken measures to decrease the number of ULPT agencies, but did not succeed in eliminating them. Why is there still some ULPT agencies and why do tourists participate in those tour? This article offers an explanation from the dual perspective of both economics and psychology. By using the application of serval models, it shows how ULPT agencies can survive by using low price. And the theory of Mental Accounting helps to explain why customers are likely to be attracted by ULPT agencies. Lastly, the article provides suggestions on how to reduce the negative impact and loss brought by ULPT agencies.