I have a one year old so who uses nebulizer but nw he sometimes cough w/ a harsh sound,will i use then the nebulizer?

Depends: on the reason for the cough. Generally a "barking" or harsh cough is not indicative of bronchospasm but more suggestive of croup, swelling of the upper airway. When I hear that a child with asthma tends to also have a harsh cough, my first thought is that there may be some silent reflux sensitizing the upper airway. Ask his primary care physician to consider that.