Distributed systems could be more secure with distributed trust model based on PKI (public-key infrastructure). The format of certificate may be different among different PKI systems. Those differences may disturb some applications performing verification of the certificate chain. In this paper, how those differences work during mutual verifications is analyzed with the new concept “certificate-format-compatibility”. Moreover, a new distributed trust model based on bridge CA (certificate authority) with high compatibility is designed out. Using this trust model, the mutual connections between entities in different trust domains would not be affected by the different certificate formats.