In a blog post by Jenny Thai here: How Asana uses Asana: Building and scaling a global content program - The Asana Blog she talks about how she made a Master Content Calendar project that “will allow you to bring all of your team’s content tasks and dependencies under one umbrella”.
How did she do that?
She probably has a project called “Master calendar” and all content are multi-homed into into (which means each task is part of their original project + this master project). Then using the calendar view will give you a master calendar.
Hi @Nima_Djoo and welcome to the Forum!
@Bastien_Siebman is right here, my colleague Jenny has created a “Master project” in which she has multihomed all tasks of all her Content projects, this way she can see all projects in one calendar view!
With that said, if all your projects are nested in the same Team, you can also refer to the Team Calendar 
Hope this helps! Let me know if you have any follow-up questions!