The invention relates to the technical field of medicine synthesis, in particular to an isoguanosine intermediate, a preparation method of the isoguanosine intermediate, an isoguanosine compound, a preparation method thereof and a downstream product thereof. An isoguanosine intermediate includes at least one of compounds represented by formula (1), a pharmaceutically acceptable salt thereof, a solvate thereof, a polymorph thereof, and a tautomer thereof, where R is a straight-chain alkane group. According to the present invention, through the isoguanosine intermediate, the final isoguanosine compound has good lipid solubility, and can enter cells in a large amount, such that the cell uptake rate is improved, the bioavailability of the compound is improved, the anti-enzyme degradation effect of the compound is good, and the treatment effect of the compound is improved. The preparation method of the intermediate greatly reduces the generation of isomers, greatly improves the conversion rate, reduces the purification difficulty of the intermediate, and is convenient for large-scale production.