The invention discloses a pH sensor, and a preparation method and applications thereof. The pH sensor comprises a matrix prepared from carbon fiber, and a hydrogen ion sensitive membrane layer, wherein the hydrogen ion sensitive membrane layer is arranged on the outer surface of the matrix. The pH sensor possesses at least one of the following advantages: the pH sensor is a solid-state electrode, glass film packaging is not necessary, and the pH sensor contains no electrolyte, so that damages on living organisms caused by sensor breakage caused by glass film breakage or electrolyte leaking in in-vivo detection are avoided; the matrix is prepared from carbon fiber, so that it is beneficial for electrode microminiaturization, and the wound area in in-vivo detection is reduced; and the pH sensor possesses high selectivity and sensitivity on hydrogen ions, and rapid response is realized.