High-fracture-strength and high-gas-tightness thin-film gas-pressure sensors were fabricated using a silicon oxycarbonitride polymer-derived-ceramic (SiCNO-PDC) material via a multiple polymer-infiltration-pyrolysis (PIP) process. To obtain dense SiCNO ceramic films, two types of liquid polyvinylsilazane (PVSZ) precursors were chosen; a high-ceramic-yield precursor with high viscosity (PVSZ-1) was designed to construct the skeleton of ceramic film, whereas a relatively high-ceramic-yield precursor with low viscosity (PVSZ-2) was designed to infiltrate in ceramic defects. The results confirmed that the PVSZ-2 can effectively fill both intergranular and intragranular defects of ceramic films pyrolyzed by the PVSZ-1, and produce the sponge-like structures with nanosized pores. Although the density of the ceramic films only increased by 2.2%-5.2% after PIP process, the gas tightness was fundamentally improved, and all ceramic films after PIP process could keep gas-tight condition without loss of pressure after 72 hours. Similarly, the fracture strengths of the ceramic films after PIP cycles have also been improved, and the value could reach 108 MPa after only three PIP cycles. In addition, because a linear relationship among the load, resonant frequency, and deflection was detected in our ceramic films, the wireless passive gas-pressure sensors with high-sensitivity and high-temperature resistance have been fabricated. It strongly indicates that the ceramic films obtained by our PIP process have real potential to be used as thin-film gas-pressure sensing elements in high-temperature and high-pressure fields.