The study deals with the relation of substitution, which is one of the constructional linguistic ties that contribute in textual cohesion by forming a textual net which helps interpreting and understanding the text. Substitution works at grammatical and lexical levels to achieve textual cohesion. Understanding the substituted items is achieved by returning to the previous ones. The problem is represented in finding substitutional expressions in the Qur'an texts and identifying their types as it is not an easy task for those who are not specialized with Arabic and Qur'anic studies as well as revealing to which extent they can achieve textual cohesion inside surah to avoid redundancy which resulted from repetition. This study aims at finding the role of substitution in the Qur'anic textual tying and achieving textual unity in order to enable readers to read the Glorious Qur'an and to facilitate its understanding for native and non-native speakers or readers and finding out the Qur'anic miracles, styles and systems through cohesive devices as well as knowing the way of textual building and cohesion. The study depends on two hypotheses which are: 1- substitution is a prominent device in cohesion which works at the grammatical and lexical levels and 2- the Glorious Qur'an has a variety of these devices which plays a vital role in tying texts in their surah grammatically and lexically to facilitate understanding without repetition. The adopted model in the study is Halliday and Hassan (1976) who suggest the types of substitution. The study depends on descriptive and analytical methodology which describes the ties of text that lead to consistency and cohesion.