In the system of computer network collaborative defense (CNCD), defense agents newly added to defense network lack of historical interaction, which leads to the failure of trust establishment. To solve the problem of trust bootstrapping in CNCD, a trust type based trust bootstrapping model was introduced. Trust type, trust utility and defense cost was discussed first. Then the constraints of defense tasks were gained based on the above analysis. According to the constraints obtained, we identified the trust type and assigned the initial trustworthiness to defense agents (DAs). The simulated experiment shows that the methods proposed in the present work have lower failure rate of tasks and better adaptability.