RESUMEN
Orthogonality and optimality of run order are two important and worthy to be considered criteria in design of experiment. For the mixed-level designs commonly used in the case of unequal levels of factors in the experiment, both orthogonality and optimality of run order are taken into account at the same time in this paper. The construction methods of mixed-level designs with orthogonality and relatively minimum or maximum level changes are respectively proposed. Based on such designs, the orthogonal main-effect plans with relatively minimum or maximum level changes are obtained by the method of collapsing factor. The designs with relatively minimum or maximum level changes constructed in this paper guarantee the cost minimum or the time trend most robust in the actual experiment arrangement.