The present invention relates to a method for preparing nickel sulfate using low-nickel ferronickel is disclosed. The method comprises the following steps: (1) grinding ferronickel to obtain ferronickel powder, and then sintering the ferronickel powder with an oxidant to prepare ferronickel oxide powder; (2) adding sulfuric acid to the ferronickel oxide powder prepared in step (1), mixing, heating, and washing with water to prepare a sulfate salt water washing solution; (3) adding a base to the sulfate salt water washing solution prepared in step (2) to adjust the pH value, then adding a fluoride salt to form a precipitate, filtering to remove the precipitate, and drying the filtrate to obtain nickel sulfate. The method provided in the present invention can improve the efficiency of preparing nickel sulfate, reduce the loss of nickel, and prepare nickel sulfate with high purity, the content of Ni potentially reaching 19.73%-21.34%.