Mid-infrared laser has very important applications in many fields such as laser communication, remote sensing, spectroscopy and countermeasure. Methods of producing mid-infrared lasers are introduced. Progress and characteristics of mid-infrared laser technology are summarized. The discussion includes two aspects. One is the linear methods such as the solid laser, semiconductor quantum cascade laser，free-electron laser and chemical laser. The other is the nonlinear ways based on second-order nonlinearity such as the frequency-doubled laser and optical parametric laser. Finally, the status and the prospect of mid-infrared lasers are analyzed.