I want to know that my BG is B+ and my wife BG is B+ than is it possible that my baby has BG O+?

Yes it's possible:
Two O blood type parents can produce a child with only O blood type.
Two parents with A blood type can produce a child with either A or O blood types.
Two parents with B blood type can produce a child with either B or O blood type.
One parent with A and another with B can produce a child with A, B, AB or O blood types.
If one parent has A and another has AB, they can either produce a child with A, B or AB blood types. If one parent has A and another has O, they can either produce a child with A or O blood types.

Genotype (DNA) Blood Type
AO or AA A blood type
AB AB blood type
BO or BB B blood type
OO O blood type