Abstract: Flows around stationary and in-line oscillating circularcylinder in uniform flow at Reynolds number of 150 is studied by solvingNavier-Stokes equations on a moving grid system which described by ArbitraryLargangian-Eulerian (ALE) method. The main objective is to investigate thelift and drag features and vortex shedding modes through different reducedoscillating frequencies and a little strong amplitudes, where the ratio ofamplitude and diameter A/D is from 0.3 to 1.2. Present numerical resultsshow that there are several modes of vortex shedding such as symmetrical Sand anti-symmetrical A-I, A-III and A-IV modes. Through analysis of previousand present results, the region of lock-on is extended, which is dividedinto five sub-regions. Especially, the force on the circular cylinder atanti-symmetrical A-I mode shows more complex characters than the originalmode. Based on the experimental and numerical results, we suggest that theradio of maximum acceleration Af_c^2/Df_s0^2 should be animportant parameter for vortex shedding modes, especially for thesymmetrical S mode.