Composite case made of brittle T800HB carbon fiber is sensitive to stress concentration, and easily cause case dome failure at low pressure. In order to overcome redundant mass of longitudinal layer of cylinder section induced by traditional carbon cloth and UD cloth reinforcement,isostrength reinforcement method is used. Φ150 mm pressure case is treated as study object, stress equilibrium factor in processing design of composite case is referred, and composite thickness in quantitative isostrength reinforcement is concluded by comparison about strain result and experiment result. As a result, quantitative isostrength reinforcement is practicable and reliable.Burst pressure of T800HB carbon fiber case using isostrength reinforcement method totally achieves design value, and longitudinal layer strength in cylinder is not redundant. The method can increase PV/W of case,especially high length-to-diameter ratio case.