This paper covers the trajectory optimization design problem of a class of demonstration flight test vehicles. Different from the traditional “once downward” movement principle of negative attack angle, the “twice downward” lower trajectory is proposed based on a SQP algorithm to meet the requirement for validating thermal protection materials. Furthermore, an important advantage of this presented method, compared to the traditional method, is that both trajectory constraints and attitude control constraints are considered. An engineering example is also given to show the advantage and effectiveness of this method. This paper covers the trajectory optimization design problem of a class of demonstration flight test vehicles. Different from the traditional “once downward ” movement principle of negative attack angle, the “twice downward ” lower trajectory is proposed based on a SQP algorithm To meet the requirement for validating thermal protection materials. Furthermore, an important advantage of this presented method, compared to the traditional method, is that both both trajectory constraints and attitude control constraints are considered. An engineering example is also given to show the advantage and effectiveness of this method.