Aiming at the low response sensitivity and the cross sensitivity of fiber grating pH sensors, a pH sensor based on fiber grating with extremely large tilt angle (Ex-TFG) is proposed, and the sensor is coated with pH sensitive intelligent hydrogel. The responsive mechanism of the Ex-TFG pH sensor is studied theoretically, factors affecting the sensor sensitivity are analyzed, and a method to improve the measurement sensitivity is presented. Combined with the unique response performance of pH sensitive intelligent hydrogel, sensors are designed and fabricated, and corresponding experiments are conducted as well. The experimental results show that, compared with the pH sensors based on fiber Bragg grating and long period fiber grating, the pH sensor based on Ex-TFG can effectively improve the pH response sensitivity (with maximum of -0.718 nm/pH) and expand the pH detection range. The measurement sensitivity of the pH sensor can be enhanced when we increase the coating thickness of hydrogel.