A new automatic design method of optical thin film systems is presented, in which the effect of the errors in monitoring of optical multilauer coatings on the performance is considered. The merit function in the design involves not only the optical properties but also the rate of finished products of the multilayer coatings by computer simulation, and the highest rate of finished products is taken as the end optimization goal. The thin film systems designed by this method not only satisfy the rezuirement of optical properties but also have larger manufacture tolerance. Hence, this method will be very effective in production. Some examples of the designs of broad-band and double-band antireflection coatings are given. The resnlts of such designs are satisfactory.