This paper presents research on fine-tuning large-scale base models, which is essential for building expert models tailored to specific tasks and domains. Specifically, we propose PiCa (Parameter-efficient Fine-tuning with Column Space Projection), a novel method for parameter-efficient fine-tuning. PiCa projects gradients of pre-trained weights onto the main column space, providing effective inductive bias for adaptation, and further improves parameter efficiency through a novel weight sharing strategy. PiCa outperforms existing state-of-the-art methods on a variety of NLP and vision tasks.