As some drench valves of foamwater spray system turn icy locally in cold winter in Haihe Tunnel, tunnel operation is effected. Based on onsite temperature measuring and date analysis, heat dissipating capability is calculated and heat power is measured, and then various insulation measures for drench valves in different parts of tunnel are made. Some conclusions are drawn as follows: (1) The isolating measure should be taken for drench valves of foamwater spray system used in cold area. (2) The isolating measures for drench valves should be adapted to local conditions and carried out according to the temperature outside the box. (3) The drench valves at the position of tunnel gate should be warmed by electric heaters. (4) The heat loss of drench valve with electric heater is inversely proportional to the temperature in the tunnel, i.e. the lower the temperature, the greater the heat dissipation and energy consumption.