The invention discloses an EPS (Expandable Polystyrene) infrared pre-foaming process. The EPS infrared pre-foaming process comprises the following steps: selecting Longwang B-SB as a pre-foaming raw material; feeding 8 to 9kg of Longwang B-SB, and setting the pre-foaming temperature into 110 DEG C; waiting for 1 to 2 seconds until the raw material is completely stable; charging dry saturated steam at the temperature of 130 to 150 DEG C and under the pressure of 0.5 to 0.6Mpa, so as to preheat the raw material; performing infrared radiation on the raw material; maintaining the temperature at 110 DEG C for 1 to 2 seconds after the infrared radiation is finished; finishing the pre-foaming of the Longwang B-SB; standing for 2 to 3 seconds, and then discharging the pre-foamed Longwang B-SB. The EPS infrared pre-foaming process has the advantages that the infrared heating is continuous, stable and easily controlled; foaming particles are uniformly heated and cannot be locally overheated to result in different size; the infrared foaming heat is transferred from inside to outside, which is different from the heating process of steam heating from outside to inside, so that the preheating efficiency is high.