Variable spray is one of the important ways for precision applying pesticide. In the past decade, great progress has been made in the technology and applications of variable spray. A comprehensive review of current research was presented in following categories: detection technology of variable spray system, control technology of variable spray system, and integration of spraying system. On the detection of crop morphology and density, ultrasonic method for detecting crop morphology was discussed and the error analysis of ultrasonic detection of crop morphology was carried out, the characteristics of ultrasonic technology and laser technology used in crop morphology detection were compared, and the advantages of LIDAR (Laser imaging detection and ranging) used for the detection of structural characteristics and canopy of trees and the superiority of LAI (Leaf area index) introduced to characterize the crop density were specially emphasized. On the detection of crop diseases, insect pests and weed, and the features of some information analysis techniques such as SOM (Self organizing maps), ANN (Artificial neural networks) and SVM (Support vector machines) etc. used for detecting crop diseases, insect pests and weed were summarized. A point was emphasized that the characteristics of crop cultivation and management should be combined with the detection of crop diseases, insect pests and weed. In terms of variable spray servo system, the existing variable nozzle and its control technology was generalized, and using the control technology to improve the performance of low cost devices and equipments was highlighted. Finally, the integration of spraying systems was also summarized and the development direction of the variable spray technology was pointed out.