The stresses, microbending loss, and changes of refractive index simultaneously induced by axial strain, thermal loading, and hydrostatic pressure in a tightly jacketed double-coated optical fiber have been studied. The lateral pressure and normal stresses in the glass fiber, primary coating, secondary coating, and jacket are derived. Also presented are the microbending loss and changes of refractive index in the glass fiber. It is shown that the stresses, microbending loss, and refractive index changes of the tightly jacketed doubled-coated optical fiber are proportional to the axial strain, temperature drop, and hydrostatic pressure; and that they are functions of the thickness and material properties of the coatings and jacket. The coatings and jacket should be suitably selected to minimize the microbending loss of the glass fiber. It is found that the Young’s modulus and Poisson’s ratio of the primary coating should be decreased, but that the Young’s modulus and Poisson’s ratio of the jacket should be increased. In addition, the Young’s modulus of the secondary coating should be increased, while the Poisson’s ratio of the secondary coating should be decreased. In the selection of thickness, the secondary coating thickness should be decreased, but the thickness of the jacket should be increased. Nevertheless, there exists an optimum value for the thickness of the primary coating.