In this paper, we choose 33Σ+1 as an intermediate state and obtain relevant vibrational spectra by scanning the frequency of PA laser. It is found that the production rate of ultracold 85Rb133Cs molecules in the lowest vibrational state, formed by short-range PA, is larger in 33Σ+1(v=3) than other vibrational states, the corresponding rotational constant in 33Σ+1(v=3) is abrupt and the energy is close to 23Π0－(v=14) state. All of these display the characteristic of resonant coupling between these two states. After the optimization of PA laser intensity and photoionization power, the production rate of 85Rb133Cs molecules in X1Σ+(v=0) is measured to be around 1.5×104/s. With the consideration of the parity of the molecular wave function and the selection rules,we find that 33Σ+1(v=3,J=1) intermediate state has the passway that can spontaneously decay to ground state of ultracold 85Rb133Cs molecules via single pass which is meaningful to explore on direct transfer from atom to molecule using stimulated Raman adiabatic passage.