The invention discloses a narrow linewidth 10mum long wave infrared laser, relates to a long wave infrared solid-state laser and belongs to the field of optics. The problem that output spectrum of theexisting 10mum long wave infrared laser is relatively wide in linewidth is solved. According to the laser, pump light is incident upon a pump light input mirror through utilization of a coupling system and transmitted pump light is incident upon a nonlinear crystal, thereby obtaining 10mum laser and 2.6mum laser; the 2.6mum laser is incident upon a long wave output mirror and is reflected to a short wave output mirror, part of the 2.6mum laser is output, and the residual 2.6mum laser is reflected to the long wave output mirror; and the 2.6mum laser reflected to the long wave output mirror passes through the nonlinear crystal, is reflected to a volume grating through utilization of the pump light input mirror, is reflected to the pump light input mirror through utilization of the volume grating and then is reflected to the nonlinear crystal, thereby obtaining 2.6mum laser and 10mum laser, the 10mum laser and the residual pump light are incident upon a dichroscope, the residual pump light is reflected out, and the 10mum laser transmits the dichroscope and then is output.