Evolution of agronomic practices has led to the classification of paddy production machines. Specialized machineries also imply differences of functional performance among different types of soil engaging tools. Each class of rotatory tiller knives thus needs to be developed with its specific optimized designs. Puddling is an independent mechanized field operation. Puddling knife has been well evolved from long history of paddy production and industry development. However, proper definition on mechanized puddling and the design theory for puddling knife is lacking. An inverse engineering approach was adopted to quantify the geometric parameters of a market available puddling knife. Puddling operation and the design principle for puddling knife was defined. A rotary tiller knife (modeled R245) was used for comparison purpose and a field experiment was conducted to illustrate functional performances of the puddling knife. Results showed that rank intrusion effect was a key factor guaranteeing the functionality of puddling. Therefore, the key parameter of puddling knife design was defined as side blade rank angle. It was the integrated effect of the side blade rank angle and the side blade width that determined the puddling performance of the knife. Compared with R245, the puddling knife was featured with its side blade rank angle, which static value was higher than the dynamic value. While the R245 had a flattened side blade (i.e. 0° of rank angle). In the front blade section, both the puddling knife and the rotary tiller knife had a similar geometry. Field experiment further proved an improved performance of the puddling knife as compared with R245, either in puddling quality and straw burial. The result also implied the need to apply inverse engineering tools for the design of all other types of soil engaging tools.