The invention relates to a wide field fluorescence imaging laser illumination device and a usage method thereof. The device comprises an excitation light source unit, an optical unit, a microscopic unit and a mechanical unit, wherein the excitation light source unit is used for providing excitation light to a sample; the optical unit comprises a first reflector, a second reflector and a third mirror and is used for changing an optical path propagation direction of the excitation light; the microscopic unit is used for completing fluorescence imaging of the sample; and the mechanical unit is used for setting the first reflector, the second reflector and the third reflector and adjusting the translational freedom degree and rotational freedom degree of each of the reflectors.