The invention discloses an environmental testing device applied to a complex stress condition, and solves the problems that complex stress application tasks such as complex environments such as temperatures, humidity, mycete, salt mist and the like and multi-axis multi-freedom degree vibration stress and the like cannot be carried out simultaneously by adopting an experimental device in the priorart. The environmental testing device comprises an environmental strengthening box with a mounting hole, an equipment mounting base arranged at a mounting hole position in the environmental strengthening box, a mounting fixing part arranged around one circle of the mounting hole, an elastic sealing ring of which an inner ring is hermetically connected with the equipment mounting base and an outerring is hermetically connected with the mounting fixing part, and a vibration generation system which is arranged on the outer part of the environmental strengthening box and is used for driving the equipment mounting base to be vibrated. The environmental testing device is designed by utilizing thinking design of multi-layered isolation and technical integration, and complex stress application tasks such as temperatures, humidity, mycete, salt mist and multi-axis multi-freedom degree vibration stress can be carried out simultaneously.