The invention discloses a portable welding pen, which belongs to the field of welding and cutting technique. The portable welding pen comprises a powder tube filled with a thermit, an ignition head on the head part of the powder tube, and an ignition segment between the ignition head and the thermit, wherein the tail part of the powder tube is closed by a clamping end with external threads on oneend; the ignition head is made of red phosphorus; the ignition segment adopts thermit welding pyrophoric powder; the thermit contains an exothermic agent, a slagging flux and an alloying agent; the exothermic agent contains CuO powder 60 to 70 wt% and Al powder 15 to 20 wt%; the slagging flux contains CaF2 powder 4 to 8 wt% and CaSO4 powder 5 to 7 wt%; and the alloying agent contains ferromanganese powder 1 to 3 wt% and ferronickel powder 2 to 4 wt%. When in use, the welding pen can be used for welding and cutting workpieces by withdrawing the pen tube, screwing the pen tube on the clamping end, holding the pen tube and then igniting the ignition head at the front end of the welding pen. The welding pen has low manufacture cost, and is small and portable. The welding pen is particularly suitable for the welding and cutting operation of steel and copper materials under emergence conditions, and has the advantages of high welding quality and high cutting speed.