A six-degree-of-freedom non-decoupling mechanism tail end pose error compensating method in a time-varying temperature field is provided. The method comprises steps of: establishing a deformation error database related to an external object; determining the actual position of the tail end of the external object after the temperature of the temperature field changes; comparing the actual position and the ideal position of the tail end of the external object to determine the positional deviation value of the tail end of the external object; determining an adjusted value required to be adjusted of the position of the tail end of the external object according to the deviation value of the external object and the deformation error database; and adjusting the position of the tail end of the external object by using the six-degree-of-freedom non-decoupling mechanism according to the adjusted value required to be adjusted of the position of the tail end of the external object. The compensation of the micro change of the position of the tail end of the six-degree-of-freedom non-decoupling mechanism caused by the six-degree-of-freedom non-decoupling mechanism time-varying temperature field external object module error compensation method in a stable inconstant state due to thermal expansion and contraction can improve the motion pose accuracy of the external object.