Let B σ 2,∞ denote the Besov space defined on a compact set K ⊂ R d which is equipped with an α-regular measure µ. The critical exponent σ * is the supremum of the σ such that B σ 2,∞ ∩ C(K) is dense in C(K). It is well-known that for many standard selfsimilar sets K, B σ * 2,∞ are the domain of some local regular Dirichlet forms. In this paper, we explore new situations that the underlying fractal sets admit inhomogeneous resistance scalings, which yield two types of critical exponents. We will restrict our consideration on the p.c.f. sets. We first develop a technique of quotient networks to study the general theory of these critical exponents. We then construct two asymmetric p.c.f. sets, and use them to illustrate the theory and examine the function properties of the associated Besov spaces at the critical exponents; the various Dirichlet forms on these fractals will also be studied.2010 Mathematics Subject Classification. Primary 28A80; Secondary 46E30, 46E35.