In view of the low sensitivity of existing optical fiber sensors in measuring temperature and magnetic field intensity, a optical fiber temperature and magnetic field sensor based on optical signal is proposed. The sensor designed has a long period fiber grating (LPFG) cascaded short period fiber Bragg grating (FBG) as the sensing structure. The magnetic fluid is used as magnetic sensitive material. The sensitivity is improved by using HF solution to etch the optical fiber cladding. Firstly, the principle of measuring temperature and magnetic field intensity by this sensor is introduced. Then, the LPFG-FBG sensor structure is simulated by using Optigating simulation software. Finally, the sensor is desinged and the experiments of measuring temperature and magnetic field intensity is conducted according to the simulation results. The experimental results show that the sensitivity of the sensor is 85.7 pm/℃ when the temperature is 35~85 ℃. When the magnetic field intensity ranges from 4~20 mT, the sensitivity of magnetic field intensity is 65 pm/mT, and the stability is good.