With the continuous development of the construction industry, the current construction production mode is gradually transforming into the contractor, professional subcontractor and labor subcontractor’s “main-sub contractor” cooperative production mode in the market segmentation. Long-term cooperation between contractors and subcontractors is beneficial to both parties, yet only limited research has explored the factors that determine contractors’ willingness to cooperate with subcontractors on a long-term basis. This paper explores the factors that influence contractors’ willingness to cooperate with subcontractors in the long term and the forming mechanisms. To achieve this goal, this study combines the characteristics of the construction industry to increase the variable of past experience, constructing an extended planned behavior theory model. Through questionnaire surveys, contractors with experience in subcontract management were surveyed, and the hypotheses were tested using structural equation modeling techniques. The results showed that contractors’ long-term cooperation intention was mainly influenced by attitudes, subjective norms, and perceived behavioral control. While past experience, a new variable, had significant effects on attitudes and perceived behavioral control, influencing contractors’ long-term cooperation intention by affecting attitudes and perceived behavioral control, past experience had no direct effect on subjective norms. This study will explain the formation mechanism of the general contractor and subcontractor’s long-term cooperative relationship and provide a theoretical basis for the general contractor to select partners and suggestions for subcontractors to improve their work.