The integrated pressure,temperature,and relative humidity sensors with high precision are highly needed in environmental monitoring and industrial control,for they have the superiorities on small sizes,low weights,low costs and easy to produce. Based on MEMS technology,a novel high precision integrated pressure,temperature,and relative humidity sensor is developed and its design principle and composition are introduced. Then,the fabrication process sequence and experiments for the integrated sensor are given. The 5.5 mm×3.5 mm×0.8 mm sensor chip consists of a piezoresistive Pt pressure sensor using adhesive bonding with SU-8,a Pt resistance temperature sensor and a capacitive humidity sensor.Experiments show that the pressure sensor has a linearity of 0.2% and a precision of 0.05% in square fitting; the temperature sensor has a precision of 0.3% and the humidity sensor shows the wide ranges of sensing ambient relative humidity from 25%RH to 95%RH and a linear correlation coefficient of 0.998 in 28.5 ℃. The high precisions of three sensors indicate the compatibility of the fabrication of this integrated sensor.