In this article，we analyze the history of social work's attempt to establish itself as a profession so as to see the trend of making social science as the knowledge base of direct social work practice.While，as we could see，positivistic science remains a strong force in creating a knowledge base for informing social work practice through the advocacy of single-case system design and evidence-based practice，the rise of critical reflective practice and the use of process knowledge has provided an alternative to social work practitioners and educators.We would take these two strands in social work practice as Type I and Type Ⅱ practice research respectively and argue that Type Ⅱ practice research is more promising in reaching for the expectation for producing social knowledge from “the site of practice”.Only does research from practice allow social workers to obtain more knowledge that is highly related to practice and possibly informing practice.The author would consider Sheppard's concept of “practice validity”as promising in filling the theory-and-practice gap and possibly leading to more discussion on the necessity for the formation of a practice paradigm which could help social work escape from the dangers of an unrestrained relativism.