Abstract: Aiming at forecasting design time quickly and accurately， the relationship between product design difficulty and design time was researched， and a method based on the difficulty coefficient of product design was proposed. First of all， by analyzing the difficulty representation modes of product design and combining the entropy evaluation method and expert weights method based on the correlation coefficient and standard deviation，the difficulty coefficient model of product design was established. Meanwhile， based on the enterprise database and coding technology， the relationship function between difficulty coefficient and design time of product design was determined with Matlab， and then the design time estimation model based on the difficulty coefficient of product design was established. Finally， the proposed method was verified to be applicable and available by an example and comparative experiments with existing algorithms. The results showed that the proposed method has better practicability and accuracy for design time estimation.

Key words: design time, difficulty coefficient, product design, entropy evaluation method, expert weights determination method, Matlab