Mid-infrared (3-5 μm) is in the range of atmospheric transmission window, which has broad application prospects. So far, the main way to obtain the mid-infrared radiation by solid-state lasers is based on the optical parameter oscillator (OPO) technology. The design principle and structures of new type mid-infrared lasers, especially directly pumping of mid-infrared lasers are not so complicated compared with OPO. With the development of crystal material and relevant pump sources, the directly pumping of mid-infrared lasers develops rapidly. Directly pumping of mid-infrared lasers, their key techniques and recent research advances, represented by Fe∶ZnSe laser, Ho∶BYF laser and Dy∶PGS laser, are summarized. The key and difficult points are analyzed at last.