Number of passenger depends on the number of surrounding building or the roads too? If I remove roads around station and building will be built instead of roads, will it increase the number of passengers?
Yes, the amount of passengers come from the buildings in the vicinity of the station. Removing unnecessary roads results in the town creating a building on that tile and adds extra passengers and mail to your station. Building size does matter too.
What i usually do is build the roads myself for the cities. This way you can lay down the road in a very efficient way and the town can grow faster since they do not need budget for roads. I usually create 8x2 rectangles this way and make sure i have a single tile open space between my station and the first road. It would look womething like below where S stands for station, G for grass/empty and R for road.
S,G,R,G,G,R,G S,G,R,G,G,R,G S,G,R,G,G,R,G S,G,R,R,R,R,G S,G,R,G,G,R,G S,G,R,G,G,R,G S,G,R,G,G,R,G