“…As we all know, Sturm-Liouville problem with interior discontinuous points inside an interval has been one of the important research topics in mathematical physics, such as heat and mass transfer, vibrating string problems when the string loads with additional point masses, diffraction problems, and so on (see previous studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and references cited therein). It is well-known that the spectrum of the standard self-adjoint Sturm-Liouville problem is infinite (see Zettl 16 ), and lots of researchers studied the properties of self-adjoint or non-self-adjoint differential operator, such as the deficiency indices, the dependence of eigenvalues, inverse problems, the self-adjoint realization, the oscillation of eigenfunctions, and so on (see other works 8,14,15,[17][18][19][20].…”