Abstract: To date, the proportional-integral-derivative (PID) controller tuning method for unstable time delay processes with multiple constraints have yet to be studied in detail. To address the above situations, we propose a novel modified cuckoo search (CS) algorithm for unstable time delay processes with multiple constraints. The proposed algorithm combines the basic cuckoo search (CS) algorithm and the nonlinear stochastic direct-search (NLJ) algorithm. Also, it first applies a general t-distribution sequence to initialize the population. Based on these two improvements, global search performances can be achieved. To verify the effectiveness of the proposed algorithm, we conducted simulation studies on the unstable first-order plus time delay (UFOPTD) process, the unstable second-order plus time delay (USOPTD) process, and the unstable high-order plus time delay (UHOPTD) process.