Abstract: Abstract Objective: This study was to evaluate internal adaptation and retention of Ni-Cr based crown with different coating layers of diespacer. Methods: A total of 30 intact human first premolars extracted freshly were collected. After tooth preparation，30 dies were made and randomly divided into 3 groups according to different coating layers of diespacer．Ni-Cr alloy was selected to fabricate based crowns which were cemented to teeth with polyether impression material to measure the internal adaptation．Then the samples were made of the crowns and teeth bonded with Fuji glass ionomer. After immersed in artificial saliva for a month and subjected to 10000 cyclic mechanical loading，the samples were sent to measure the maximum load at failure．Results: The internal adaptation at the three groups with different layers of diespacer had significant difference（P<0.01）；For the maximum load at failure，no significant difference was found between one layer group and two layers group（P>0.05），while both of them had significant differences compared with three layers group（P<0.01）．Conclusion: Coated with one or two layers of diespacer on the die could improve internal adaptation and retention of Ni-Cr based crown significantly.

Key words: internal adaptation, diespacer, retention, glass ionomer, Ni-Cr based crown