We perform atomistic molecular dynamics simulations on the binary blends of entangled polyethylene wherein short probes are dilute in long-chain matrixes as well as on their monodisperse counterparts. Compared to monodisperse systems, the relaxations of the end-to-end vector of short probes are retarded for the suppression of constraint release (CR) on blending, and the suppression degree becomes weaker with increasing of probe length. A parameter reflecting the CR strength is introduced, and its critical value from no CR at all to CR taking effect ranges from 0.071 to 0.46. By subdividing the overall motion into the lateral and longitudinal motions, we find both motions are more restricted in blends, and the time scale for the onset of these differences or of CR effects is smaller than the overall relaxation time. Additionally, retardation on blending behavior is further confirmed by the probability distribution of the chain entanglement lifetime.