Based on the tests of sixteen unbonded partially prestressed concrete beams under low cyclic reversed loading, the constitutive relations under cyclic loadings of every material were selected reasonably. After an in-depth analysis on the mechanical characteristics of unbonded partially prestressed concrete beams, unbonded prestress actions were converted to their equivalent loads by setting short rigid arms. Then, a nonlinear full range hysteretic analysis method for unbonded partially prestressed concrete beams was proposed by combining the step deforming method and the step loading method, and a MATLAB program was developed. Through comparisons and analyses, the calculated results coincide well with the testing results. So it has theoretical and practical engineering significance.