Seamless Passenger Airbag Door, which means the seam of the passenger airbag door is not visible to the passenger, is being frequently implemented in the instrument panel because of its good surface appearance. But it is always a challenge to design a robust passenger airbag door with an invisible seam because many kinds of failures are possible during the design, such as cracks of the substrate of instrument panel, hinge failure of airbag door, windshield breakage, etc. Besides the engineering difficulties, the simulation of seamless passenger airbag door deployment is challenging due to three aspects: 1. the simulation method of the early stage airbag deployment (0~20 msec after trigger), 2. the material model of the airbag door pre-weakening line (the invisible seam); and 3. the physical measurement of the reaction load between cushion and door. In this paper, the FPM (Finite Point Method) method in PAM-CRASH™ was used to simulate the early stage airbag deployment and the fabric material model was validated by a material sample tensile test. An airbag deployment test was designed to push a mass upwards and the acceleration of the mass was measured. The measured acceleration shows FPM method with the validated fabric material model is capable to give a good prediction of the early stage airbag deployment. The material model of door seam is also presented and validated with a physical test. To measure the reaction load between airbag cushion and door, Flexi-Force™ sensors, film-like pressure sensors, were used. To deal with the nonlinear signal output of the sensor in different pressure ranges, a calibration device was developed exclusively for this sensor. After the calibration, 32 Flexi-Force™ sensors were put into a seamless passenger airbag door on the IP structure, and then the reaction load between the airbag door and the cushion was measured in its deployment. The action point position of the resultant reaction load, its peak value and duration correlate with the physical tests. Finally, the limitations and future developments are discussed.