Aiming at the problems of low automation, low pesticide utilization and poor adaptability of orchard spraying equipment in northern China, an orchard variable distance spraying equipment based on crown volume estimation was designed. The spraying arm of the equipment could adjust the spraying distance and height in horizontal and vertical directions under the control of the control system, so as to adapt to the characteristics of fruit trees in different orchards. In order to achieve precise spraying, a sensor array was constituted by infrared ranging sensor to detect the crown. The data measured by sensor array was used to build a tree crown volume estimation model by mathematical method, and the adjustment scheme of spray parameters was designed to make the spray distance and spray volume adjusted accordingly. In order to verify the performance of the spraying system, the actual movement time and the response time of the spraying arm when received the movement command and the accuracy of the crown volume estimation model were tested. Two groups of automatic target spraying tests of fixed distance and variable distance were carried out on simulated peach trees. The results showed that the movement of the spraying arm could achieve the instantaneous response and the actual movement time was almost consistent with the theory, and the relative error of the volume estimation model was 11.27%. Compared with the fixed distance target spraying, the variable distance automatic target spraying increased the pesticide attachment rate by 18.66%, and saved 30.25% of the liquid medicine.