The dependence of a fiber Bragg grating strain sensor on the improved structure parameters was investigated both numerically and experimentally. The stress distribution and the strain of the grating region was obtained. In the case of the overall width and thickness are equal, the sensitivity of this structure is about 600 times higher than the traditional I-shaped structure. The influence of the 6 key structure parameters on the strain sensitivity and the measurement range was analyzed in detail. Experimental results were also given compared with the numerical simulated results. The gratings were packaged respectively with UV glue and glass solder to get the sensitivities were: 249 pm/N, 330 pm/N and 1.1 pm/N. The analysis method and data provided a basis for structural optimum design of fiber Bragg grating strain sensors in different applications.