Location spoofing detection is an important part of location proof schemes in IoT systems. It is important for location systems to accurately evaluate the credibility of location data uploaded by users. Differ with the works employing physical layer features such as signal strength or channel state information, we focus on laying the foundation for solutions aiming to build the location spoofing detection functions in the blockchain based IoT systems. More specifically,an IoT system is established at the node level and the moving-track level for the evaluation of the credibility of location proof with the characteristics of the blockchain positioning system. A multi-layer fuzzy Analytic Hierarchy Process (AHP) evaluation method is considered for the detection of location spoofing in blockchains. The simulation results show that the proposed scheme is practical, and can provide a reference for the credibility evaluation of location proof.