Abstract: Service innovation network carries the characteristics of interpersonal relationships, highly embedded knowledge and lacking of formal intellectual property protection institutions. These characteristics enable serve firms to choose informal relational governance mechanisms to promote knowledge exchange and profit protection. However, the relational perspective cannot capture the complex and dynamisms of service innovation network, which need more comprehensive study of the joint effects of the contract-based governance and relational-based governance. Extant literature offers conflicting views regarding the effects of governance mechanisms on knowledge acquisition and service innovation. Based on a survey of 308 knowledge intensive service firms, the study addresses how relation-based governance mechanism and contract-based governance mechanism affect knowledge acquisition and service innovation. The results show that relation-based governance has positive effect on knowledge acquisition. Knowledge acquisition has the mediating effect between relation-based governance and service innovation. Moreover, relation-based governance and contract-based governance have a negative joint effect on knowledge acquisition. The findings provide important theoretical and managerial implications for collaborative innovation strategy in service sector.