A series of 2D direct numerical simulations were performed with an accurate level set method for single drop impacts. The adopted ACLS method was validated to be efficient with perfect mass conservation in both normal and oblique impacts. A square-root correction for neck bases was modified in accuracy as well as scope of applications. In addition, process of jet formation and evolution was studied to reveal internal dynamics in drop impacts. It's found that pressure gradient and vortex are coexisting and completive reasons for jet topology while the inclined angle has a significant effect on them. Mechanisms of jet formation and evolution are different in the front and back necks. With the help of PDF distribution and correction calculation, a compromise in the competition is observed. This work lays a solid foundation for further studies of dynamics in gas-liquid flows. (C) 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.