The invention discloses a floater variable resistance sensing type tunnel ponding warning device which comprises a float chamber, wherein through holes in upper and lower ends of the float chamber are covered with filter screens, a floater is arranged at the bottom of the float chamber, the floater is wrapped with a magnetic material, a varistor clings to the scale value part of the float chamber, a variable resistance wire is fixedly mounted inside the varistor, and the variable resistance wire is sleeved with a magnetic variable resistance slip ring. The invention provides a prewarning and displaying device for ponding conditions occurring inside unattended tunnels and culverts, and before a vehicle enters the tunnels and the culverts, prewarning and state displaying to the ponding conditions inside the tunnels and the culverts can be given in a full position, so as to remind a vehicle driver. Therefore, road traffic accidents caused by ponding in tunnels and culverts can be avoided, the problems in traffic and road safety, caused by ponding on traffic roads provided with tunnels and culverts can be effectively solved, and traffic road running safety is enhanced.