The underwater thermal glider utilizes ocean thermal energy to change its buoyancy,which enables it to ascend and descend.A Phase Change Material (PCM) as the working fluid inside the thermal engine tubes is sensitive to the surrounding seawater temperature,whose effects are different with the various displacements and gliding angles of the glider.In this paper,the effects of the displacement and the gliding angle on the performance of the thermal engine were studied numerically and experimentally.On this basis,the ways to eliminate the negative effect of a thermocline on the performance of the thermal engine were obtained.The results show that the displacement and gliding angle affect the transition time of the PCM.There exist the threshold values of the displacement and gliding angle for the normal work of thermal engine.There are two means of eliminating the negative effect of a thermocline on the performance of the thermal engine and improving glider performance:one is to increase the displacement,and the other is to decrease the absolute value of the gliding angle.There is also another better way to improve glider performance.