Linear active disturbance rejection control (LADRC) is a new control method used to handle a system's external unmeasured disturbance and internal unknown uncertainty. Its essence is to transform the uncertainty of a system into an observable state and utilize the extended-state observer to estimate in real time and compensate it using a state-feedback control law. In this paper, under the constraints of a specified robustness measure and the integral time squared error, a tuning formula of the first-order LADRC is proposed for the first-order process with the dead time model. Then, the tuning formula is tested for a variety of benchmark systems and a temperature control experiment. Finally, the performances are compared with the conventional simplified internal model control-PI tuning method. The simulation results verify the feasibility of the first-order LADRC tuning formula and expand the formula's application in the field of industrial control.