System identification is a method for using measured data to create or improve a mathematical model of the object being tested. From the measured data however noise is noticed at the beginning of the response. One solution to avoid this noise problem is to skip the noisy data and then uses initial conditions as active parameters, to be found by using the system identification process. In the first part of this paper describes the development of the equations for setting up the initial conditions as active parameters, and then the simulated data as well as response data from actual shear buildings were used to prove the accuracy of both the algorithm and the computer program, which include the initual conditions as Active Parameters，are precise.
