The laser hardening technology used for crankshaft is introduced and the investigation on surface hardening of a nodular iron crankshaft was carried out by using a kW CO 2 laser system.By building the temperature field mold,we explained the phenomenon that the laser hardening depth is not dispersed averagely along the direction of laser movement on laser hardening crankshaft neck . By this temperature field mold we can optimize technical parameters of laser hardening on computer directly instead of by conditional methods. Theoretical calculation is consistent with the experiment.