Based on the high temperature and refractive index sensitivity of long period fiber gratings (LPFGs) and the high reflection efficiency of the fiber Bragg grating (FBG) filters, a temperature and refractive index sensor was designed, which is a cascaded LPFG based on the FBG filter. The temperature and refractive index were measured by using the FBG filter to reflect partial power of interference wave of the cascaded LPFG into the power meter. In this paper, the feasibility of the cascaded LPFG based on FBG filter temperature and refractive index sensor was analyzed by the signal superposition principle. Then, the binomial fitting was done between the power meter readings and changes of the temperature, and the power meter readings and refractive index. The determination coefficients are 0.9990 and 0.9959 respectively. The high stability of the proposed sensor was also tested. These results show that the cascaded LPFG based on FBG filter temperature and refractive index sensor could be used for the precise measurement of the temperature and refractive index and has a high stability.