A graph is edge-transitive if its automorphism group acts transitively on its edges.In this paper,we give a characterization of connected edge-transitive trivalent graphs of order ℓp,where p is a prime andℓ(0<ℓ<p)is an integer.Applying this characterization,we first give a classification of connected semi-symmetric trivalent graphs of order ℓp with 0<ℓ≤54 and p a prime,and then we show that all connected edge-transitive trivalent graphs of order ℓp with 0<ℓ≤100 and p a prime are known.