Abstract: This paper introduce a fast size measurement system for pear fruit. By using computer digital image processing technology，an indirect digital measuring model based on standard objects was firstly built，then，a size measuring software kit of pear fruit phenotypes was developed by using AForge.net class libraries and MatLab image processing tools. Finally，the artificial measuring results were used to check the model and the software kit. Measurement results of software kit showed no significant differences with the control（manual measurement），neither in the case of single/multiple object（s）in one image file，nor in the case of fruits with different sizes. The software kit could be used to identify and measure multiple phenotypes of multiple pear fruits accurately in one 2D picture precisely，such as fruit height，fruit width，fruit shape index，fruit sectional area，fruit core height，fruit core width and stalk length，etc. In addition，this size measurement system is rapid，accurate and easy to use，which could be applied for the phenotypic analysis of other similarly sized fruits，like peach & tomato，and for other organs，such as seed and leaf. Besides，the image acquisition device and image editing tools can help researchers to establish normative phenotypic image data sets，which should be promote the standardization and informationization of phenotypic analysis work.

Key words: pear, fruit, size measurement, standardization, image processing