In this paper, the method of caculating multifractal spectrum with partition function is briefly introduced based on multifractal theory. As research object, a growing structure is simulated by computer. Then we discuss the shortage of the partition function method and the effection of free scale zones to multifractal spectrum results. At last, a new approach is presented to express developing surface structure. It can describe the character of developing surface structure more exactly, and will play an important role in analyse and characterization of complex structure.