The invention discloses a movable platform limit measuring instrument and a measuring method. The measuring instrument comprises a sensor positioning device, a detection frame, a first sensor, a second sensor, an inclinometer, an encoder, a power supply and a host, wherein the first sensor is arranged on the sensor positioning device and transmits the acquired platform section data to the host; the second sensor is arranged on the detection frame and transmits the measured gauge data to the host; walking wheels are arranged at the bottoms of two ends of the detection frame and can move along atrack; the first sensor, the second sensor, the inclinometer and the encoder are respectively connected with the host; and the first sensor, the second sensor, the inclinometer, the encoder and the host are respectively connected with the power supply. According to the movable platform limit measuring instrument and the measuring method, the actually measured limit size, the gauge and the line ultrahigh value of the platform can be accurately acquired, and the actually measured limit size is compared with a preset limit threshold value so as to judge whether the platform invades the limit ornot.