The invention discloses a device and method for guaranteeing rainy-day driving safety at a mountain-wind crossing road section. The device comprises a laser rainfall detector, a wind-speed and wind-direction detector, a data processor, an emitting and receiving antenna and an LED variable-information message plate. The method specifically comprises the steps that meteorological data of the mountain-wind crossing road section of a highway in a mountain area is collected; a short time window is taken as an updating cycle; divided monitoring sections are established according to different road line types; meteorological data along the route of the divided monitoring sections is collected in real time, wherein the meteorological data includes rainfall, wind speeds and wind direction angle parameters; means of the meteorological data in the short time window are calculated; one this basis, safety representation values of the divided monitoring sections are calculated; a driving safety speed-limiting value is solved based on the safety representation values; safety speed-limiting schemes are formulated; and speed-limiting information is released in combination with the variable-information message plate in real time.