After defeat in Russia in 1812, Napoleaon was being chased by the European Allies across central Europe and into France by early 1814. The Prussian and Russian forces were led by the Prussian Marshal Blucher and were threatening Paris by early 1814. Napoleon was fighting for his very survival.
After several battles on the trot, some won, some lost, Blucher occupied the town of Laon. Laon was trategically important because it was a major communications crossroads near Paris. Holding Laon would give Blucher the logistical base to attack into Paris. Napoleon obviously felt it could not remain held by the enemy. Laon was also a tactical stronghold due to its placement on a plateau with steep slopes for defense.