Crowd simulation has a wide range of applications, such as travel network planning, evacuation planning and layout design [Feng et al. 2016]. A critical issue in crowd simulation is to simulate crowds at different moments. In [Krontiris et al. 2016], an influence map based on attractors is used for authoring activity-centric crowd simulation. However, the desired crowd distributions are not considered. Specifically, given that the desired crowd distributions are input at different time instances, we would like to simulate the crowds between these time instances. In this work, we propose an approach for crowd simulation editing, aiming for simulating crowds between different time instances. The users can draw the attractive regions and non-attractive regions. Then our system automatically computes the paths and simulates the crowd movement based on a Markov decision model. Our system is applicable to crowd authoring, animation and layout design.