Abstract: Standard coal sample was hardly obtained as worse sampling of broken coal sample，and coal strength was tested by field In-situ measurement in field，but the problem that probe leaped forward unapparent appeared during broken coal strength testing with drilling in-situ penetration method.An experiment was done in Xinyuan coal mine, where coal fractures developmental，and drilling in-situ test with different diameter probes were tested，the diameter were 6, 8 and 10mm，respectively，fitting analysis of different diameter probe loading and oil pressure data in drill hole was done，which diameter is 132mm，the relativity of two was worse as diameter was 6mm，the fitting degree increased with probe diameter increased，and the relativity of two increased obviously as diameter was 10mm.And the test also done in drill hole that diameter was 56mm，the testing data showed that probe leaped forward could be improved with probe diameter increased, but the rising rate of testing data effectively rate，and the results also influenced by hole diameter，the testing effectively rate in large diameter hole improved about 10% than in small diameter hole.