Advances in science and technology are creating huge benefits and value for society. The digitalization of the world has brought great changes to human being’s daily life. Meanwhile, the increasing degree of digitalization has led to an unprecedented explosion of data, resulting in increasingly severe information storage challenges. According to the current developing trend, the global data volume is expected to reach 175 zettabytes by 2025. With the rapid growth of global data volume and the exponential growth of total data, the existing storage methods will no longer be able to meet the storage needs brought by the digitalization of the world and then there is an urgent need to develop information storage methods with better storage performance, higher storage efficiency and more durable storage media. Nature has offered a powerful solution by using DNA molecules as carriers of information, where genetic information has been transferred stably more than a million years. DNA storage has many advantages over traditional storage media, including high storage density, potentially low maintenance costs, and ease of synthesis and chemical modification, which make it an ideal alternative for information storage. The current process of storing data in DNA includes six main steps: encoding, writing, preservation, retrieval, reading, and decoding. Among them, the writing of data is the basic for realizing the storage of data in DNA, concluding writing data in DNA sequence and in DNA structure. In this review, we first introduce strategies for in vivo data writing in DNA storage systems, which primarily involve writing data into DNA sequences and DNA structures. This is followed by an overview of the development of in vivo writing techniques in DNA storage systems. Finally, we discuss the challenges faced by DNA storage systems in terms of high writing costs and slow writing speeds, and prospects for large-scale synthesis of high-purity DNA and improved biocatalysts.