I want to reduce large numbers of draw calls for my android game.
it hangs in playing and making performance issue. 
You can reduce draw call by implementing these things
batching dynamic and static
Texture atlases,
Occlusion culling
lightmaping
mobile friendly shaders
low poly objects
low number of particles
unity already defined what to do for mobile performance
and by my experience i also used free unity plugin called Draw call minimizer and in give video they show how they reduced draw calls from 69 to 12.
The answer to this question pretty much sums up most things. A simple search would’ve unveil it 
I, too, suffered from draw calls, reaching 4-5K for my PC title. A little experience, some testing, profiling, and trying things at runtime pretty much leads you to the source of the problem.