Thermosonic bond is widely used in package of semiconductor chip due to its advantages, such as simple process, high efficiency, and no pollution. Ultrasonic play important role inspired interconnection interface atomic energy and soften metallic materials in thermosonic bond. The vibration of bond tool is nonlinear and bond strength is unstable with contact interface condition changing due to discontinuity characteristic parameters of contact interfaces. In order to improve bond strength of chip, model of ultrasonic propagation across a rough contact interface was established. Aluminium wire bond was performed on a thermosonic bond test platform. The harmonic waves of bond tool and the bond strength were measured. The experiment results show that the best bond strength and the less higher order harmonic is achieve when the contact interface pressure is in moderate range.