In order to reveal the performance of solid fuel ramjet (SFRJ) quickly and accurately, a model with thermal calculation in the chamber was presented. By calculating the position of normal shock in the inlet, the performance of the inlet, combustor and nozzle was obtained with coupled method. Based on VB, the universal software for the engine performance calculation was developed. A model of solid fuel ramjet extended-range projectile was employed and the calculation results agreed well with experimental data. The results indicate that the engine performance can be rapidly predicted with this method, thus to reduce design period and satisfy the precision demand in the schematic design.