Semidilute poor solvent polymer solution is investigated by the method of Ursell-Mayer cluster expansion. Series and ring-form diagrams are considered for polymers to calculate the osmotic equation of state of the solution, and this equation is shown to be the same as obtained by Edwards by a different method. The static structure factor, which is the Fourier transform of the correlation function of the system, is also calculated in the same approximation; the first term of this factor corresponds to the Jannink-de Gennes result by the random phase approximation. The osmotic compressibility equation, which connects the osmotic pressure and the correlation function, is considered to check the consistency of our results and confirm the validity of the present approximation. Effects of the excluded volume on the equation of state and on the structure factor are investigated up to the first order of the excluded volume parameter z. It is shown that the excluded volume does not affect the osmotic equation of state as well as the structure factor in this approximation.