Lightweight cryptography is implemented in unrolled architecture generally, which has the characteristics of low latency and high real-time performance but also faces the threat of Side-Channel Attack (SCA). Different from traditional loop architecture, the unrolled architecture requires separate protection against SCA in each round. This leads to the unrolled architecture that is very sensitive to the number of rounds that need to be protected against SCA. In this paper, we propose an optimized method for the chosen-input attack that can effectively increase the number of rounds of differential propagation and recover the key from the fourth round of unrolled PRINCE for the first time. This research also evaluates the hardware overhead and performance of two types of Threshold implementation (TI) for PRINCE. The experimental results indicate that TI imposes substantial hardware overhead on the circuit, therefore a specified number of protection rounds is required.