Poly(vinyl chloride sulfone) was prepared by copolymerizing vinyl chloride (VC) and sulfur dioxide (S). The copolymerization was initiated by N,N′-azobisisobutyronitrile, and formed poly(vinyl chloride sulfone)s with average VC:S molar ratio n⩾1.0. Their thermal degradation behaviour has been investigated by thermogravimetric analysis (TGA) and mathematical simulation. The thermogravimetric and differential thermogravimetric curves of poly(vinyl chloride sulfone) were measured over the temperature range of 100–500 °C at 10 °C/min under nitrogen. Poly(vinyl chloride sulfone) decomposition can be described with four consecutive reactions. The fourth-order Runge–Kutta method was used to solve the differential equations arising from this kinetic scheme; thermogravimetric curves were modelled on this basis using a computer simulation. The activation energy, the frequency factor and reaction order of thermal decomposition of poly(vinyl chloride sulfone) can be obtained by dynamic TGA measurement.