Internet of Vehicle (IoV) is a promising Internet of Thing (IoT) application, where roadside unit (RSU) plays an important role to transmit traffic information to cloud server through internet. However, there exists redundancy among the data collected with a data collection period by a single vehicle, which may cause network congestion and waste the storage of cloud. In this paper, we propose to equip each RSU with a mobile edge computing (MEC) server, and differential compress data at edge node, for saving the transmission time and storage space. First, we present a new cost model for COPY/ADD class, then a metric to measure a differential compression algorithm is given. we propose a Maximal Length of COPYs (MLOC) algorithm that can construct a good delta encoding based on our cost model and evaluation. Theoretical analysis proves that the proposed MLOC algorithm constructs a delta encoding with minimal amount of COPYs on the premise of maximal total length of data segments copied. Numerical results show that MLOC algorithm can get better performance in constructing a good delta encoding between two data compared with Simple Greedy algorithm and Hash Suffix Array Delta (Hsadelta) algorithm.