The invention discloses a radial jet bit pressure controller which comprises an upper joint (1), a spring (3), a force bearing sleeve (4), a central tube (5), a sliding sleeve (6) and a lower joint (7), wherein the upper joint (1) is fixedly connected to the upper end of the central tube (5), the central tube (5) is arranged in the force bearing sleeve (4), the upper end surface of the force bearing sleeve (4) and the lower end surface of the upper joint (1) are in limit fit, the sliding sleeve (6) is glidingly arranged in the lower section of the force bearing sleeve (4), the lower joint (7) is fixed at the lower end of the sliding sleeve (6), the central tube (5) is sleeved with the spring (3), and two ends of the spring (3) are propped between the force bearing sleeve (4) and the sliding sleeve (6). By means of ballast control by the spring, application of the bit pressure is stable and controllable, the technical problem of difficulty in window cutting operation due to instable bit pressure is solved, and the success rate and efficiency of the radial jet drilling technology are increased. The invention further discloses a bit pressure controlling method.