In order to solve the problem of delayed or lost sampled value（SAV）in substation，a self-adaption packet-loss-based SAV estimation algorithm is proposed. According to the transmission characteristics of SAV and applying Lagrange，the realization flow chart of the quadratic SAV estimation algorithm and selection method for synchronous interpolation time are especially studied. With experimental data obtained from single-phase grounding fault simulation in PSCAD，the estimation accuracy of the algorithm is confirmed by MATLAB software. Especially，the estimation error is analyzed in detail. Research results show that this algorithm has high estimation accuracy for several SAV estimation. Therefore，embedding this algorithm in normal relaying algorithm can be very useful to solve the hidden danger caused by delayed or lost sampled values，which is in favor of stable and reliable operation of substation.