An approach to generate linear frequency modulation laser source based on an optical phase modulator and a tunable optical filter was proposed. A narrow linewidth fiber laser seed source was modulated by an optical phase modulator, whose driven ratio frequency (RF) signal was generated by the microwave linear frequency modulation signal with a fundamental frequency, and thus a series of wideband linear frequency modulation laser signals were generated. A tunable optical filter was used to select the desired linear frequency modulation optical sideband and suppress the others modulation sidebands. The experimental results show that when the optical filter retains the positive second order modulation sideband, a linear frequency modulation laser signal with a tuning range of 2 GHz and tuning rate of 6 THz/s is obtained. The instantaneous linewidth of the linear frequency modulation laser signal is 3.2 kHz in 1 ms observation time. The system is simple in structure and easy to implement. This technique has important significance for the applications such as frequency modulated continuous wave laser radar and coherent spectroscopy.