Molecular dynamic method has been applied to a single polymer chain immersed in a solvent. The interactions for the pairs, of two solvent molecules (SS), of a chain element and a solvent molecules (CS), and of two non-neighbor chain elements (CC) are given by the Lennard-Jones potential, and the interaction between two bonded chain elements is given by a harmonic potential. We changed the CS interaction parameter ${varepsilon}_{CS}$ to 0.5, 1.0 and 2.0 times of the SS interaction ${varepsilon}_{SS}$. We calculated the pair correlation functions for the SS, CS, and CC pairs, end-to-end distance and radius of gyration with the varying ${varepsilon}_{CS}$ parameters. The results showed that a phase separation occurs between the polymer and solvent in the 0.5 system where ${varepsilon}_{CS}$ = 0.5 {varepsilon}_{SS}$. The autocorrelation functions for end-to-end distance and radius of gyration were also calculated.