Oxidizer has a decisive influence on the exothermic capability of the exothermic/insulating riser sleeve. After analyzing the ingredient of the imported exothermic/insulating riser sleeve, three sorts of commonly used sylvite oxidizers (A,B and C) was selected and the influence of their mixture ratio on the ignition time, exothermic duration and the exothermic power of the riser sleeve was investigated. The results showed that the exothermic capability of the riser sleeve containing single oxidizer was not obvious. The exothermic power of the riser sleeve made with the mixture consisting of 3%~6% A, 1% C and 2%~4% B achieved the level of imported products or was even slightly better than the latter.