A projection-based incompressible smooth particle hydrodynamics (ISPH) is applied to the simulation of the deformation process of viscous liquid drop. In our numerical computation, the particle shifting technique is used to overcome particle clustering due to the tensile instability in SPH. In order to verify the proposed ISPH, numerical simulations of a viscous circle drop stretching and a viscous square drop rotating are carried out. The pressure distribution in the drop is obtained, and the deformation process of viscous liquid drop is correctly captured. Comparisons between numerical results and the analytical solutions in the literature are presented. The simulation results show that the projection-based ISPH with particle shifting technique can be used to simulate the deformation process of viscous liquid drop with stability and accuracy.