In the design and construction of ultra-high peak power laser systems, it is necessary to control the accumulated B-integral of the laser pulse, but currently there are no reasonable B-integral control standards for picosecond and femtosecond lasers. We systematically evaluate the influence of the B-integral on the output capability of picosecond and femtosecond laser systems for the first time, taking Nd:glass lasers and Ti:sapphire lasers as examples. For picosecond lasers, the temporal domain compressibility and the small-scale self-focusing effect restrict the B-integral to 1.7 and 1.9 respectively. For femtosecond lasers, the B-integral is mainly restricted by the small-scale self-focusing effect and the far-field focusability, which limit the B-integral to 1.5 and 1.7 respectively. The restriction made by far-field focusability can be largely relaxed by inserting a deformable mirror. The study of the factors restricting the B-integral will provide guidance for the design of ultra-high peak power laser systems.