The invention discloses a method for measuring a nonuniform temperature field in a wall and the wall thickness, and the method comprises the steps: phase differences separately measured by using an ultrasonic longitudinal wave method and an ultrasonic transversal wave method are obtained, the phase differences are used as the input quantity, the equivalent thermal boundary condition and wall thickness are obtained based on a multiparameter inversion method of the inverse heat conduction problem, and the temperature field distribution states of the furnace wall or tube wall in different times are obtained according to the direct heat conduction problem. The method can be used for measuring the nonuniform temperature field in structures such as a blast furnace wall, a high-temperature steam pipeline wall and the like under a wall thickness unknown condition.