In order to improve the CPU utilization of spacecraft computers, the new generation of spacecraft operating system uses a hybrid scheduling algorithm that includes both fixed-point starting tasks and sporadic tasks. Among them, fixed-point starting tasks are often safety-critical tasks and need to be started at fixed points and cannot be blocked during execution. Under the condition that fixed-point starting tasks and sporadic tasks coexist, the existing real-time lock protocols cannot guarantee that the blocking time of fixed-point starting tasks is zero, so on the basis of the classic priority ceiling protocol, a real-time lock protocol based on the idea of avoidance blocking is proposed in this study to ensure that sporadic tasks’ access to shared resources will not affect the execution of fixed-point starting tasks by judging in advance and setting virtual starting point. At the same time, by temporarily increasing the access priority of some resources, the cost caused by task preemption can be reduced. This study presents the worst blocking time of the above lock protocol and uses the schedulable rate experiments to analyze its performance. Experiments show that in the case of short critical sections, this protocol can control the schedulability loss caused by accessing shared resources to under 27%.