In this paper, the tritium–tritium fusion reaction rate in a muonic molecular ion (µtt) is calculated by using a square-well nuclear potential as a complex for nuclear interaction between two tritones. The complex potential parameters are obtained by fitting process on fusion cross-section experimental data. The real and imaginary parts of the nuclear potential are calculated as Ur = −62531.87 (keV) and Ui = −165.63 (keV), respectively. A free parameter that is related to the radius of this potential is A = 0.004155. Also, considering the optical nuclear potential, the energy value of µtt muonic molecular ion is calculated. The fusion rate is calculated by liner combination of atomic orbital (LCAO) method. Finally, the reaction rate, λ, is obtained 0.28 × 1010 s−1 by calculating the transition probability through the potential barrier and the oscillation frequency of wave function
