In order to make the fiber grating sensor have the functions of temperature/strain dual-parameter sensing and communication transmission in the application of fiber sensing system, a new flat-top fiber grating sensor structure composed of the chirped long period grating(CLPG) and chirped fiber Bragg grating(CFBG) was proposed. The sensitivity coefficient matrix of temperature and strain of the sensor was established by measuring the displacement of the center wavelength, and the theoretical analysis and simulation were carried out. The results show that, the temperature and strain sensitivities of CLPG were 2660 pm/℃ and 132 pm/με, respectively. CFBG sensitivities were 12.6 pm/°C for temperature and 0.8 pm/με for strain. Both CLPG and CFBG had flat-top output spectra at the same time, and the flat-top spectral bandwidths reached 13.8 nm and 5.6 nm, respectively. The sensor can realize the simultaneous sensing of both parameters of temperature/strain and has a stable communication transmission band. This study serves as a reference for the application of fiber grating sensors in fiber sensing systems.