Within the quasi-one-dimensional effective potential model and effective mass approximation,we obtain the wavefunctions and energy eigenvalues of the ground(j=1) and first 2 excited states(j=2 and 3) of a donor impurity in a rectangular GaAs quantum dot in the presence of electric field.The donor impurity-related linear and nonlinear optical absorption as well as refractive index changes for the transitions j=1-2 and j =2-3 are investigated.The results show that the impurity position,incident optical intensity and electric field play important roles in the optical absorption coefficients and refractive index changes.We find that the impurity effect induces the blueshift for j=1-2 and redshift for j=3-2 in the absence of the electric field,but it leads to redshift for j = 1-2 and blueshift for j = 3-2 in the existence of the field.Also,the optical coefficient for the higher energy transitions j =2-3 is insensitive to variation of impurity positions,while that for the low energy transition j =1-2 depends significantly on the positions of impurity.In addition,the saturation and splitting phenomenon of the optical absorption are observed as the incident optical intensity increases. Within the quasi-one-dimensional effective potential model and effective mass approximation, we obtain the wavefunctions and energy eigenvalues ​​of the ground (j = 1) and first 2 excited states (j = 2 and 3) of a donor impurity in a rectangular GaAs quantum dot in the presence of electric field. the donor impurity-related linear and nonlinear optical absorption as well as refractive index changes for the transitions j = 1-2 and j = 2-3 are investigated. The results show that the impurity position, incident optical intensity and electric field play important roles in the optical absorption coefficients and refractive index changes. We find that the impurity effect induces the blueshift for j = 1-2 and redshift for j = 3-2 in the absence of the electric field, but it leads to redshift for j = 1-2 and blueshift for j = 3-2 in the existence of the field. Als, the optical coefficient for the higher energy transitions j = 2-3 is insensitive to variation ofsence positions, while that for the low energy transiti on j = 1-2 depends significantly on the positions. In addition, the saturation and splitting phenomenon of the optical absorption are observed as the incident optical intensity increases.