Exciton binding energies in InGaAsP/InP quantum well with different contents of In are calculated through variational method in the effective mass approximation. The variation of exciton binding energy as a function of well width, In content, and applied external electric field is studied. It is shown that the exciton binding energy is a non-monotonic function of well width. It increases first until reaching a maximum, and then decreases as the well width increases farther. In addition, with the increase of In content, the well width should increase to reach the maximum value of exciton binding energy. It is also found that the external electric field has little effect on binding energy, but when the electric field is large enough, it will destroy the excitonic effect. These results may provide some theoretical basis for the design and control of InGaAsP/InP optical devices.