Sensor-cloud has gradually developed into a research hotspot. A good trust evaluation mechanism can better address some security issues in this new structure, such as internal attacks. A good trust evaluation mechanism can also ensure the security and efficient transmission of information in this structure. After an extensive research on sensor-cloud and trust evaluation mechanisms, it was found that trust evaluation mechanisms in sensor-cloud can be divided into two categories, among entities and in entity. After comparing the advantages and shortcomings of existing trust evaluation mechanisms, a new fog-based trust evaluation mechanism was designed and future research directions of trust evaluation mechanisms were discussed in sensor-cloud