Provided is a lamp with a drainage channel, including an outer case, a lamp module, and a rear cover. The lamp module includes a heat dissipation case having a mounting portion, and at least one light emitting elements and a reflector are sealingly mounted in the mounting portion. The heat dissipation case other than the mounting portion is provided with one drainage hole, and the lamp module is assembled at one end of the outer case so that water or liquid penetrated into the outer case, or water condensed in the outer case can be discharged through the drainage hole. The rear cover is pivotally coupled to the other end of the outer case to close or open the other end of the outer case so as to prevent the sensitive electronic components from being exposed to the outside and not to be adversely affected by environmental factors when repairing or changing the setting of the operation mode.