Geographical knowledge search and innovation have attracted much attention in recent years. Yet the existing literature placed much emphasis on the way firms search for new ideas and knowledge as well as the geographical dimensions of knowledge sourcing without taking accounting into the nature and characteristics of knowledge per se. We examine the relationship between knowledge search and product innovation in both low and high‐tech industry with a survey data from China. While both internal and external knowledge search are conducive to product innovation of high‐tech firms, only external knowledge search is valuable for low‐tech firms. External unrelated knowledge is significant for innovation of high‐tech firms whereas external related knowledge search is significantly enough for low‐tech firms. It highlights the importance of knowledge relatedness in innovation and appeals a shift of theoretical focus from ‘how to search’ and ‘where to search’ to ‘what to search’ in the process of innovation.