The activity in project can be split into multiple sub-activities in batches of smaller granularity execution in the real production project planning and scheduling environment to shorten the total projects makespan. For the preemptive multi-project scheduling problem with activity splitting, the patterns of activity splitting and recombination are discussed from the perspective of collaborative optimization, three heuristic rules for the activity splitting judgment are proposed, such as long activity duration(LAD), long project makespan(LPM) and high resource rate(HRR), and a heuristic algorithm for solving multi-project collaborative scheduling problem with activity splitting is designed. Simulation results show that the method can shortn the total makespan of the multi-project scheduling problem by activity splitting.