Generic programming has emerged as a paradigm for the development of highly reusable and safe software libraries. Generic constraints mechanism includes a collection of features for constraining generic parameters and verification of the validity of generic parameter instantiated, thereby guarantees dependability and safety of generic programs. This paper first reviews the current research status of generic constraints, exposing the difficulty of describing and verifying generic programs with dynamic semantic constraints. Based on a new description of generic constraints of Apla language, it then proposes three main types of generic constraints mechanism: constraints of basic data types, constraints of custom abstract data types and constraints of subroutines. Next, with the help of Isabelle theorem prover, the paper designs the generic constraints matching detection and validation algorithms and further gives the implementation scheme of generic constraints mechanism in PAR platform. It confirms that the proposed generic constraints mechanism can solve a series of complex generic constraints problems, and so markedly improves dependability and safety of generic programs.