Based on the traditional mass evaluation model, an iterative evaluation model to study the fuel mass and the take-off mass of tactical scramjet missile is devised, and an improved evaluation model is put forward by taking terminal guidance into account. By comparing these two kinds of evaluation models for fixed and moving targets, the source of evaluation error is achieved. The influence of range, target speed, distance of terminal guidance and cruise height on evaluation error is discussed. The simulation results show that the traditional mass evaluation model which ignores the terminal guidance is suitable for short range fixed targets and low speed targets, while the mass-evaluation model considering terminal guidance or modified model ignoring the terminal guidance are suitable for long range, high cruise height, long-distance terminal guidance and high speed targets.