The invention is applicable to the technical field of electrical elements, and provides a surface-mounted type trimming capacitor and a trimming method thereof. The trimming capacitor comprises a topmetal plate, a middle metal plate and a bottom bonding pad; the top metal plate and the middle metal plate form a first capacitor unit, the middle metal plate and the bottom bonding pad form a secondcapacitor unit, and the first capacitor unit is connected with the second capacitor unit in parallel; the top metal plate comprises a connection plate and at least one trimming plate connected with the connection plate, and dielectric substrates fill the positions between the top metal plate and the middle metal plate and between the middle metal plate and the bottom bonding pad. The connection ofthe trimming plates of the top metal plate and the connection plate can be cut off so as to change the relative area of the top metal plate and the middle metal plate, and the capacitance of the first capacitor unit is changed; and the area of each trimming plate is fixed, so that the capacitance trimming amount can be effectively controlled through the structure and the method mentioned above, the operation difficulty of capacitor debugging is reduced, and the production efficiency is improved.